Greens, fruits, veggies, grains, protein. Offer stuff like collards, bok choy, kale, apples, oranges, carrots, peas, oatmeal, wheat bread, cheerios, monkey chow, dog food, they'll eat almost anything organic (and a few things that aren't organic

). Just pick out a variety of healthy foods and they'll eat it. Avoid lettuce cause they're mostly water. Fresh food is always better than frozen.
I have a variety of other pet foods I have around, so I offer a little of each to my crix. My gutload consists of pheasant chow, rat pellets, hamster food, collards, bok choy, dandelions, dog biscuits, fish food, vitamin/calcium supplements, and of course the nasty veggies from my dinner plate, and my left-over apple cores, etc.