If you have a compost pile the soldier fly larvae and pupae are one of the highest natural sources of calcium that chickens love to eat. The pupae look like dark trilobites or some sort of prehistoric life form. They are usually in the dirt away from anything fresh and new in the pile. You can freeze them and feed them all winter.

My chickens always loved left over human food - preferring a cooked squash over a fresh one, so I would cook up odd casseroles of veggies and cereal and plop it on the ground for them to demolish.

Try sorghum, vigorous as all heck and will survive almost anything, easy to harvest or you can leave it standing and let the chickens harvest it. It also makes a good grain for human consumption, cook it like brown rice, it tastes like almonds but has about the same nutritional content as other whole grains. Chewy and tasty.

Corn. You can grind it a little since some chickens won't eat it whole-kernal.