Here's a great resource:
http://www.fsis.usda.gov/wps/wcm/connect/19013cb7-8a4d-47...
What matters most is proper storage, proper thawing, and proper cooking.
Store cold or frozen foods in an insulated bag in your car (in the warm weather), to make sure that when you're driving home from the store, or if you have another errand, the food stays cold.
At home, remove plastic packaging and shrink wrap. There's air in the package (especially those packages with the stiff plastic wrap that have an inch or so of space between the plastic and the meat). Air is the enemy (affects quality and can cause spoilage). So, at home, with clean hands, remove the meat from the package, and re-wrap tightly (air-free) in good freezer paper or plastic wrap, then place in freezer-type zip-top bags. Squeeze the air out. Label with the meat type and the date you bought it. Then refrigerate it, or freeze it if you're not going to use it right away.
Make sure your fridge and freezer are set to the proper temps: no more than 40 degrees for the fridge (about 35 or 37 is good), and 0 for the freezer.
Thaw frozen foods in the fridge, and make sure that meats are on the bottom shelf of the fridge (in case any liquid should drip from them - they won't drip or leak onto other foods).
Example: you buy a whole chicken at the store. It has a "sell-by" date of today. Put it in one of those cold-storage grocery bags (the insulated kind) since it's a hot day outside, and when you get home, remove the chicken from its packaging. If you're using it tonight, simply refrigerate it in a zip-top bag, with any marinade or seasonings. If you are going to cook it tomorrow or the next day, re-wrap in good plastic wrap and a freezer zip-top bag. Then, place the chicken in your fridge which is properly set at between 32 and 40 degrees. The danger point is even a tiny percentage higher than 40 degrees. Then a day later, or up to 2 days, you cook the chicken. Or, put the chicken in the freezer for a couple of weeks, properly wrapped and labeled.
Another example: you buy a frozen package of steaks at the store, and the date to use it or freeze it is today. Again, keep it cold in your car in an insulated bag if it's a hot day. Then remove the steaks from their packaging, wrap in freezer paper, place in freezer bags, and transfer them to your freezer for a couple of weeks. The freezer is properly set to 0 degrees. When you are planning to eat the steaks, transfer them to your fridge in order to let them thaw. Since your fridge is at the right temp, this is safe.
Since you have properly stored and packaged the meats, they are safe. You don't have to panic about those dates, as long as you store the food safely. The dates are not the dates that the meat will spoil, they are your guide for using and storing and preparing the meats. The dates will also give you a clue as to the best time to use the foods for maximum quality and taste. For example, ground beef or poultry that is near its "use by" date won't be at its peak but if properly stored and cooked, it will be fine in a sauce or chili or meatloaf or everyday burgers for a casual supper. However, if you're buying expensive steaks for a special celebration dinner, you might not want to buy the ones marked "sell by" or "use by" today. They won't be at their peak of perfection. They'd be safe to eat (if stored and cooked properly), but they might not be quite as tasty and perfect as a steak that was just butchered. I frequently buy the meats that have been marked down due to reaching their "use by" or "sell by" dates, re-package them at home, store them properly, and use them in a hearty spaghetti sauce or casserole, or in well-seasoned burgers.
As for storing the cooked chicken breasts, refer to the link I posted and see the charts at the end.