I'm not going to bother commenting on my own preferences, because I think this is so individual and personal. But the question reminded me of a book--which I'm actually pretty sure I read about here--that I've been wanting to read, called Make the Bread, Buy the Butter. I believe it addresses exactly your question--again, obviously the author's personal preferences, but you might find it helpful or interesting!

Taste and time are always personal preferences, but cost (excluding time) is quantifiable, and I second Make the Bread, Buy the Butter as a good starting point with the cost calculated for you. I'm not a huge fan of all of the recipes, but it's a good starting point for thinking about.

I second the above posts on Make the Bread, Buy the Butter! It is a great resource from somebody who experimented with this exact question, and measured success by cost and time. Sometimes it also depends on how passionate you are about cooking for if putting the time and effort is worth it to you, and the shorter shelf lives make planning more important, but another benefit is that you know exactly what ingredients are in your food.

Well, I never would have imagined that yogurt would be a) so easy to make and b) so cost effective. I can make a week or more supply of yogurt from a half gallon of milk for about $4.00 (and the initial cost of a cup of yogurt to add to the milk the very first time). The price would be lower if I were using grocery store milk instead of dairy milk. It's delicious and I can add all my own flavorings. I will never buy commercial yogurt again.

Salad Dressing is definitely a Make: a flavorful oil for creaminess (or mayo, yogurt, buttermilk, sour cream, miso or a mixture), an acid (vinegar, lemon juice, lime juice), a couple flavorings (garlic, herbs, ginger, horseradish, blue cheese, chilli sauce, chiles, parmesan... just not all of them!) and you've got a different dressing every night, with no additives, less sugar and lots more flavor.

Third vote for "Make the bread, buy the butter" - we have not purchased bread in years, and sometimes when I think I might break down and buy it I look at the price and wonder who in the world wastes $4 - $6 on organic bread?!

Another big saver is dried beans vs. canned. I make a lot of crockpot stews with beans - the beans taste better and cost a fraction of the price.

Last, I would recommend making your own salad dressings. A good bottle of vinegar and some go-to recipes for balsamic, ranch and dijon vinaigrette have saved me countless dollars.

A couple more: Pancakes are so much better than the mixes. The only "special" item is buttermilk, and there are plenty of good recipes that don't even use that.

Brownie and other cake mixes are the same thing: it's no faster to use the mix, only a few steps different.

I recently experimented with making my own almond butter due to the salmonella scare. If you have a powerful food processor or blender (like a Vitamix), then this is a very easy thing to make yourself. And you can experiment with a lot of different types of nuts/seeds.

http://vegedibles.wordpress.com/2012/10/18/i-cant-believe-its-nut-butter/

Great goal to have. Start small. What do you like eating? Veggies like tomatoes, kale, lettuce, herbs like thyme, lemon balm etc are very easy and some can even grow in cold weather. Take on no more than 1 or 2 plants at a time if you're not used to it. Start small with food as well; canning and jams are tricky for sanitary reasons. But salad dressings, lemonade, whipped cream etc, never buy those things. So easy to make at home and will taste a thousand times better!

Make: granola, salad dressing, roasted red peppers.

Mozzarella and yogurt are on my list to learn. I'd love to by more self sufficient, but I struggle with a lack of space and a black thumb.

I'd say definitely pick your battle. Time really is money some times. I won't, say, make fresh bread all the time because I don't have hours to knead it and wait for it to rise. My household of 2 cannot eat the bread fast enough before it becomes stale anyway. So to me, the time going into that is not worth it.
On the other hand, I will spend about 3 hours each time making a huge batch of homemade dumplings and freeze them. We eat them often enough. And the homemade ones are infinitely better than frozen store-bought versions that are laden with MSGs, that I feel worthwhile to devote a few hours making them.
Other things I won't buy are granola, whipped cream, cake, cookies, and salad dressing because they are so easy and takes no time to make.

Make: salad dressing, tomato sauce, hummus, beans (cook a big batch in the slow cooker and freeze instead of buying canned), ice cream (well, okay, you can buy it if you need some RIGHT NOW), most beverages (iced tea, seltzer plus syrups, etc.), veggie sausages (really easy, freezer-friendly recipe in the Vegan Brunch cookbook by Chandra Moskowitz that improves upon the expensive Field Roast brand)...

I'd say to look for things/recipes where you can throw everything into a blender or food processor and it comes out in seconds. That would include things like salad dressing, mayo, whipped cream, salsa/guac, tomato sauce (you can see it tends to be things that top main dishes). As for making your own bread or pasta, while I've done it before, it tends to be too messy and time-consuming to be worth it to me, despite the better flavor. I'll take the convenience on that stuff almost every time.

I think about the pros and cons when considering a new DIY.

Pros: If I use it often; if the raw materials can be obtained locally (or if the climate is right for growing); If it's hard to find an additive-free equivalent in stores; If it's expensive to buy.

Cons: If it's difficult to store in the quantity I would make; if I can barter with someone that's already an expert at making it; if it makes a terrible mess; if it requires specialized, expensive equipment; if I would make it so seldomly that I wouldn't have a chance to practice, tweak, and perfect my technique.

I recommend doing a personal analysis of pros and cons before choosing to jump into a DIY project. Your location and lifestyle will affect your choices. Personally, this has led me to DIY dried fruit and meats, yogurt, cheese, bread, pickles, and jams. Also DIY meat (venison), DIY veggies and fruit in the garden, and DIY eggs.

Make: hummus, tomato sauce, salad dressing, jam, cakes

So far, I make pesto (all the commercially-bought versions have cheese, and I can experiment with different greens and different nuts), muesli mixes (way too expensive, otherwise!), salad dressing (vinegarettes), and... well. That's actually about it, right now.

As soon as I get a Vitamix, though, I'm going to be adding nut butters (and Nutella!), sorbets, hummus, I kind of want to dabble with bread...

A bread machine was very worth it to me - $40 off craigslist and I make a loaf about every 2 days for me and my husband. All I have to do is put in the ingredients and pull out a fresh loaf 3.5hrs later - no kneading, no timers for rising, etc. Cheap and I know what goes in it, plus there's nothing like fresh baked bread.

I second the salad dressing, baking mixes (you can even pre-mix your dry ingredients for recipes like pancakes in bulk if you want so it's like you have a 'mix' on hand), granola (I make big batches and freeze 3/4 in ziplocs so I don't have to do it constantly), pizza dough, spaghetti sauce, etc. I've been slowly going through my pantry and attempting to replace the bottles & cans in there with from-scratch versions - I'm working through condiments to see what's worth it! I've made my own beef broccoli (Chinese takeout style) and it was amazing. I'm trying pad thai this week. I used to use jarred sauce to make them. I make ice cream with a relatively inexpensive Donvier hand-churned model I got as a Christmas gift one year.

There are some things that I don't attempt because I don't have a food processor (yet). Some things aren't worth making without one. And I have to watch it because I only have so much freezer space - I'd love to invest in another small deep freezer so I can make more from scratch and have it on hand instead of always cooking from scratch. I'd also love to try yogurt.

I started making my own soft white cheese (fromage frais) because they were always out at the store. Now I make it all the time (minimum twice a week), it's the same as making yogurt but requires straining for 24-48hrs afterward.

A lot of DIY food items take some time, but it isn't actually active time. Baking two loaves of bread takes me about 15 minutes active time, then I can just let it rise; if I have to leave or something, I put the dough in the fridge to rise more slowly. Yogurt takes time, but only a few minutes of my time; then I drain it to make Greek yogurt, which I substitute for cream cheese, sour cream, and ricotta in recipes (I also add a little sugar and use it in place of whipped cream on fruit desserts). In addition to the savings on buying these other prepared foods, making yogurt also helps me use up milk that's near its expiration date, saving me even more money.

Another one to that's definitely worth it is making stock in the slow cooker--just put bones, skin, veg, whatever in there and let it go overnight (as long as 24 hours).

Hey Michelle! I found that yogurt is really easy to make! Here's my version..
http://lifewithlampnsofa.com/2012/05/12/homemade-vanilla-yogurt/

Some impressive work going on! While philosophically I'm sympathetic to the making the bread theme, in fact I have such fabulous and varied bread available to me in the Bay Area that making my own doesn't make sense -- except, of course, to save money. But for the pleasure in eating it, we have some incredible bakeries whose bread is a joy.

Peanut butter, (freezer) jelly, and bread are all super easy to make and bring the humble PB&J to another level when combined. Quick breads (muffins, pancakes, fritters, etc) are really easy, too. Probably less than 5-10 minutes of active time once you get the hang of it. Potato chips are quick and easy as well.

I also think that the health factor has to come into it.
If you make it yourself, even if it costs a litlle, or even much, more than the commerical stuff, you at least know what has gone into it, NO HFSC, REDUCED SALT etc.
I make my own bread, butter, cheese, pasta (no palm oil in this), stocks, sauces, jams, mayonaise, salad dressings.
I am trying to find a good source for grains so i can grind my own flour.
My husband is in charge of the sausages, bacon, salamis. In fact anything that can be smoked or put through the mincer.
I make my own soap, cleaning products, laundry products.
Wish I could grow coffee and chocolate trees where we live, I would make that as well.
We no longer trust big business food companys, what producers we do use tend to be small local owner operators, like our Olive Oil lady (brilliant EVOO), friends who have chooks provide us with eggs we help out with feed etc for them, we belong to a cow co-op and get fresh milk direct from the farm.
Costs abit in time but pays off in quality and health matters, PLUS we both enjoy it and that last one is a biggy.

Agree with @ALICELOST, who says it comes down to personal taste. Here's how it shakes out for me:

Make: Bread (artisan & sandwich), pizza dough, vegetable stock, beans from dried beans, granola, pesto, jam.
Buy: Cheese, yogurt, tofu, snack-y things like crackers, most condiments, tomato sauce, canned tomatoes. (I would totally can my own tomato products if I had a garden, though...someday!)

In the "make" column, I tend to favor things that save money and can be made in advance. For instance, I like homemade mayonnaise and it is easy to make, but you can't exactly stock up on it, and if I'm making a recipe that includes mayonnaise I usually can't be bothered to add "make mayonnaise" as step one. So I rarely make mayonnaise from scratch. But since dried beans and pizza dough can be prepared and then frozen to use anytime I need, those are worth it to me.

By the way, I also really liked Make the Bread, Buy the Butter.