Aside from the "goodies" they eat while foraging our two acres, our flock is fed a vegetarian diet; vegetarian layer feed or certified organic vegetarian layer feed being their main source of required nutrients. They have free-choice access to grit and oyster shell.
For treats, our flock loves greens (veggie tops), kale, swiss chard, lettuces, red and green cabbage (they especially love the red), brussel sprouts, green beans, carrots, corn, tomatoes and all types of summer and winter squash. They go crazy for fruit like cranberries, blueberries, plums, apples, grapes and peaches. We also give them chopped hard cooked eggs, buttermilk, fat-free plain yogurt w/active cultures, low-fat or fat-free, low sodium cottage cheese and provide organic grains (rolled oats, barley, wheat) and fancy scratch, sunflower and flax seeds.
I usually chop the cranberries in the blender as we had one pullet suffer some breathing difficulties after a large piece got lodged in the back of her mouth. Don't feed apple seeds, too many can be toxic.
Most of the vegetables and some of the fruits come from our organic gardens, as did some of the wheat and sunflower seeds, as well as the corn I mentioned previously
You can plant an extra plant or an extra row of your favorite veggies for your flock.