I try to pick out the ones that are perfect size for her (if you had told me a year ago that I'd be 'playing' with roaches I wouldn't have believed it) basically the distance between her eyes. I'd say they're the 5/8 size, maybe 1/2.
I purchased chow and water crystals for them from Kimbrells, plus I put in a few food scraps (mainly carrot). Yesterday I put in a piece of nectarine and they were all over it almost before I closed the lid. But that was the first time I put in a fruit, it's usually veggies. They don't seem to eat any greens I put in.