Raw potatoes, raw beans, apple seeds or peach pits are no gos....chickens are pretty good at avoiding things that are bad for them so I wouldn't worry too much and frankly, my hens couldn't stay away from the tomato plants this summer, they stripped the stems they could reach bare and never showed any adverse symptoms, but to each his own....there is a pretty good treat list of chicken do and don't feeds in the learning center that you should check out.
Chickens will eat almost ANYTHING.....mine particulary love yogurt (which is also very good for them), guacamole, melons (fruit and seeds/innards), mealworms (any kind of bugs really) banana, cheerios, sunflower nut meats and greens.....they also like salt and vinegar chips, pizza, chili cheese fritos, cheetos, fried rice and fruit loops but I hardly ever feed them those because they are junk foods just the same way we wouldn't want to eat much of them