It took a while for my chicks to catch on to snacks, but at 8 weeks these are the things they like:
Plain Greek Yogurt (Favorite!)
Tomatoes (Especially the watery/seedy part, if they flip over so just the skin is showing, they ignore them)
Grapes (Favorite!)
Earthworms (Some go crazy for them, some ignore them)
Spiders (bugs in general)
Dried Cranberries (sometimes)
Strawberries
Ham
Clover and grass (at least, they peck at it when outside, not sure how much they're actually eating)
I tried bits of prune and lettuce tonight, but they weren't too interested.