My experience so far is that chickens will eat just about anything you give them. If they don't like it they'll spit it out.
I'm careful about giving them anything with too much salt or sugar. My chickies love it when I give them part of my PB&J or any sandwich. They follow me around until I show them my bare hands. They do learn quickly that anything in your hands is "probably a treat for them"--at least I have taught mine that (not intentionally!).
My chickens get all leftovers that haven't been eaten in three days. Along with cat food from the meal before. So far the only thing they didn't like was beet greens.