I have a few different tips you could try. First of all, when you originally cook your chicken, undercook it a little bit. Most people cook their chicken for WAY too long. Experiment by shortening the cooking time so it is still a little pink in the middle. Then when you recook it the middle should end up cooked through instead of rubbery. The second tip is to poach your chicken in some water or broth. I have found this to keep my chicken nice and moist. It is also a good way to reheat chicken. And finally, you could stop reheating your chicken by pounding a breast flat and then cooking it in a non stick pan for a few minutes on each side. This method only takes a few minutes and will fix your rubbery chicken in a jiffy! Good luck.

Thanks doll,
The Glamorous Housewife

I precook all of my lunches for the week, which usually involves chicken. I find that cooking it in a lot of moisture, as well as cutting it into smaller pieces help keep it moist. I also reheat in the microwave, with a damp paper towel on top, which helps keep moisture in the chicken (kind of like what you do when you reheat rice). Hope it helps!

Just did this yesterday. I cook a weeks worth of organic chicken breast at a time. I drizzle olive oil and sprinkle kosher salt and cracked pepper on them and then grill them on the stove top using my calphalon panini grill pan - 4-5 minutes each side. The outside gets a nice sear and then I remove them to a plate and cover with foil until cool. They stay moist and juicy this way and then I cut them up in dices and put them in individual baggies and it makes it so easy to make a salad each morning.

I throw an entire chicken (minus the inside bits) into the slow cooker (no water, no nothing - you could opt for seasonings if you want) and let it steam itself on low for 8 hours. Then I pick the meat and freeze it in 1 or 2 cup servings (to be used later in casseroles, chicken salad, etc.) Then I do a slow cooker chicken stock w/ the bones. A great weekend project that produces a lot of useful food!

We will often cook a whole chicken and need to reheat the breasts for later meals. Very gently warming the white meat in either chicken broth or a mild marinade keeps the meat juicy and can add some punch. We like using some orange juice, olives and harissa for a Mediterranean flavor or soy sauce, ginger and a touch of Sriacha for Asian. The key is to not let the liquid boil. It may take 10-15 minutes to warm a whole breast.

When I make chicken for salad or other purposes I poach it. Naturally there is a good guides to poaching chicken right here on theKitchn.

http://www.thekitchn.com/how-to-poach-ch-28367
http://www.thekitchn.com/how-to-cook-moist-tender-chicken-breasts-every-time-36891

I wonder if you could just toss it with whatever dish you're serving while that food is freshly hot and let the residual heat warm your chicken? It would only work if the chicken is in smaller pieces though.

I have has excellent luck with roasting it. If it starts out good and juicy you can reheat it without it getting too dry. I also suggest sauces.

I second the poaching option.
Last November i found boneless, skinless chicken breasts on sale for $1.85/lb. I bought a family size pack and poached them, then cut them up and froze in zip lock freezer bags. I have used some of this chicken and it is not dry or rubbery, but very convenient to use.

Agree with Glamorous Housewife's suggestion--pound the chicken breasts thin in advance, but leave them uncooked until you need them. They'll cook super-fast.

I always opt for poaching, too. My favorite tips are to brine the chicken (esp boneless breasts, which always seem dry) for an hour beforehand, and let it cool in the poaching liquid before slicing/shredding/storing. Since I started using those methods, my poached chicken has been perfect.

Have you seen this book? Recipes for cooking chicken for now and later. :)
http://www.amazon.com/Twice-As-Nice-Chicken-ebook/dp/B00AQCJLB6

Pounding and cooking quickly works at home but not on the go. I frequently reheat chicken at the office.

It's not glamorous, but I *microwave* almost any kind of pre-cooked chicken- grilled, rotisserie, whatever- in a bowl with chicken broth. I definitely lose some seasoning, but lack of moisture is worse than lack of seasoning to me.

I rarely eat the chicken alone this way. Almost all of my reheated chicken gets mixed with other food so the seasoning issue isn't such a big deal.

I HATE reheated chicken... even in a homemade soup or something. The taste makes me gag. I just use leftover chicken in a salad or something

Me, too! But only in a microwave. I have yet to hear the same thing from someone else, but I can taste when meat, especially chicken, has been reheated in a microwave. Thus all the chicken leftovers are not eaten by me! Too bad, since the convenience factor is so nice sometimes.

Two tips that I don't think have been mentioned yet:
1) Marinate (I use yogurt) or brine the chicken before cooking it to avoid that reheated chicken flavor (I agree, really gross).
2) If you are not averse to breading, try a dusting of bread crumbs or flour. The reheated meat will stay moist (unless you cut into it too soon and the juices run out).

I use these two techniques for making chicken nuggets for my toddler. The frozen nuggets heat up moist every time after a couple of seconds in the microwave.

Whole roast chicken. Season the bird well, stuff cavity with herbs, half a bulb of garlic, and half a lemon, push some more herbs and garlic under the skin of the breast, and roast in a medium hot oven (18 mins per 500g, plus additional 18 mins). It will keep for 3-4 days in the fridge, and is delicious cold.

Or Hainanese chicken:
http://www.nytimes.com/2008/09/17/dining/171mrex.html?_r=0

I tried to cook the one on this video: http://www.youtube.com/watch?v=AST04MCRKOQ
Easy enough and mmmm... tasty!! Think it is very convenient to find videos not the recepies on the net. Just download it with this app http://dvdvideosoft.com/products/dvd/Free-YouTube-Download.htm for example and here it is - the cookbook is on your PC ;)