Oh you'll get a mixed bag of conflictong answers here. There is a sticky post that lists good treats you can offer them, but it does seem toe a matter of taste or preference to the chickens. You just have to try things out and see what they think.
For my girls, I tried frozen blueberries a few times and they were curious about it but really didn't care for it. Even thawed or mashed. Now I did see them go after one that was sitting out for a couple days.
They love kale. I have it handy for our bearded dragon and they never refuse kale. The store ran out of kale once and I brought home some collard greens. They liked that too, but not as excitedly. May be more fibrous and it does have a strong aroma to it. They kind of like cabbage, but I prefer giving darker greens instead. Not so hot on carrots, but haven't tried it lately.
Gave them seedless grapes cut in half/quarters and chicken keep away was a great show. I only gave them 1 whole grapes each since they found their beaks sticky after running around in circles.
Mine love raisins!!! It seems to be their favorite treat so far and watermelon -they love it when its hot! An ear of steamed cooked corn they love to peck on also.
Can't believe I forgot about the other stuff... They love BOSS (esp 1 in particular) and scratch. Wasn't too sure about watermelon or apples, but they were gone after a while so I know they ate it.
Said good morning to them this AM with a small handful of kale and almost lost my hand. Should have had more kale.
I'm sprouting some BOSS right now, thinking it would be easier to digest than whole seeds. Should be ready in a few days.
this is simmilar to another thread, and as daft as it sounds chickens in some ways are like us, not everyone likes the same things, as i posted in the other thread my chickens love peas but hate cabbage, where as someone elses loves cabbage and hates peas!
so the trick is to try them on scraps from stuff youve eaten, you will soon find out what sends them into a frenzy or not.