I feel pretty lucky because mine seem willing to try anything. I usually pick them a bouquet of alfalfa every other day and hang in in their run and they have a great time jumping up for the tender blossoms. But they'll eat almost anything.
Sometimes I'll get a couple dozen crickets from the pet store for them and release them in the run for additional fun and exercise. They get plenty of greens and soon will be old enough to roam the yard (65'x80') with 6' fence.
I don't give treats everyday although they always expect something when they see me.
My chicks favorite treats in order from best to least: WORMS, bugs, red seedless grapes, yogurt, watermelon, spinach, scratch, zuccini...not crazy about lettuce.
Once we get done with the daily ritual of pulling weeds from the garden, they get divided up among the pens, all the chickens (and ducks) love exploring all the goodies. The chickens eat most of them. We occasionally throw in some cherry tomatoes which is a riot to watch them peck and then run around the pen with it on their beak trying to keep it away from the others. We always throw in several but of course if one chicken has one that must be the best one and all the others want it. LOL Watermelon is a huge treat. My chickens will demolish them until there is a very thin shell of the rine left.