Mine are quite spoiled, I cook extra eggs for them. They like raisins, lettuce, fresh basil, watermelon, cantaloupe . Cheese is a favorite but causes loose poops. Hot dogs, but they don't care for all beef ones. But their absolute favorite is dried mealy worms…and they like them better if hand fed!
Mine love all leafy greens, especially kale. I just tried popcorn (air pop, no salt or oil) and they didn't care for it. Doesn't mean they didn't eventually eat it though! They haven't cared much for fruits either or tomato-- but last nite they did seem more excited over tomato. Of course, dried meal worms make them INSANE to the point I'm scared to show them what I have when I walk into the run! But they are young and I don't want to give more than a little taste of a treat once each day. I feel that the greens are good for them though, so they get some nearly every day (they have no access to growing fodder in the run). But at 10 weeks, they want me to chop everything up for them pretty small..... is that normal? Maybe at their age?
Dandelion greens, my chickens love them. They are free here and grow everywhere and full of vitamins. I work at a dairy plant that makes cottage cheese, my birds love it and I've never noticed their poops being any runnier than usual. Mine love watermelon.