Being from the south pies are traditionally for dessert,but I'm learning more about meat pies (considering historically this is where they all come from) and I found these coal miner's pasties and have been wanting to try them. Mix in a few more veggies and should be a good hearty lunch for a working farmer.

I'd definitely consider the pre-industrial farmer's lunch, some thick bread, hard cheese, and cured meat. Maybe with a little mustard. Throw in a piece of fruit and it's pretty filling.

In the UK there are two traditional solutions to this. A plowman's or a pasty. Both are healthy and delicious if you use high quality ingredients.

My husband works in a different field but also needs a lot of quick non-spoiling dinner options. What about some roasted veggies and maybe some chopped up chicken or boiled eggs (all in bite sized pieces) dressed with olive oil and rice vinegar and stored in a mason jar? He could ideally eat it with a fork or just tip it into his mouth in a pinch.

A good option similar to a calzone is a pepperoni roll. It's the state food of West Virginia because Italian immigrant coal miners could take them down in the mines for lunch without refrigerating them. I add a little bit of marinara sauce to the above recipe, and you could probably add spinach or chunks of roast tomatoes or peppers to get in some vegetables.

empanadas.

Bite size foods work well when you are on the go. Fruit and veggies that are cut up and easy to pop in your mouth -- carrot sticks, cherry tomatoes, apple wedges, etc. Nuts that are shelled, trail mix and baggies of crackers make good snacking. Hard boiled eggs, steak or chicken cooked and cut into strips, cheese sticks or any other protein that he likes. If he can eat it with his fingers or shake it directly into his mouth from a jar, he can eat it while he's sitting in his tractor seat. Don't forget to send along a BIG thermos of water and throw in some wet naps or baby wipes, so he can wash his hands if needed.

Why not a Thermos to keep things safely hot and cold?

My vote goes to those pasties.

Or single-serve quiches.

Omelette muffins are portable, delicious and filling. Sometimes I bake mine with a sausage meatball stuck on top. You can mix up the flavors with various veggies, cheese, and herbs. Here's a good recipe:

http://farmfoodblog.com/grain-free-omelet-muffins/#more-1341

Why not sandwiches? Is it an aversion, boredom or spoilage issue?

I think sandwiches are my favourite lunch meal, perhaps even dinner meal too. They're really versatile and with an ice pack I don't think any mayo or cream based salad dressing would spoil by lunchtime.

Another option, though, would be mini pizzas made on english muffins or other small flatbread. They hold together well and are tasty at room temp. Depending on your choices you can make them pretty healthy too.

Also, you could do wraps to change it up a bit. Still fairly close to a sandwich, but different in certain ways that might make it more pallatable, exciting or portable.

When I know I'll have to eat at my desk, I like grilled veggie wraps. If you wrap the whole thing in plastic or foil, it's easy to eat with one hand. Hummus and strips of grilled zucchini, eggplant, and carrots are the basics. Sometimes I add avocado, deli cheese or meat, or include a tub of salad dressing to dip it in. Yum.

I'm going to echo the ploughmans, or Cornish pasty suggestions.
However, When I was at school, I would make a weeks worth of sandwiches on a Sunday night, and they'd all go in the freezer- grated cheese and pickle, mainly. I'd take a pack out in the morning, and by lunch they'd be defrosted. I think that actually you could do this with lots of things, as small eat in the hand sized things will defrost fairly quickly.