This year much of my garden is alloted to chicken feed. I'm growing the following:
Turnips, Mangels, Rutabagas, carrots, cabbage, apples, barley, oats, millet, buckwheat: These will be stored and feed throughout the Winter. Some of this is already in (turnips, mangels, barley, oats).
Dwarf Essex Rape and forage turnips: Planted in early Fall for late Fall, early Winter free-ranging. I also put a bunch of rape & turnips in 4 weeks ago for Spring free-ranging.
Buckwheat: Planted throughout Summer. Once the plant is vigorous I rotate the chicken tractor over it until devoured. I plant enough so that the tractor always has a buckwheat patch to set on. For this purpose I grow it for the plant, not the seed.
On top of this they get food scraps & garden scraps. I intentionally over plant most vegetables and just feed the extra to the chickens. They even get the scraps left over from butchering the meat chickens, and what ever is left over from our chicken-dinner.
In mid to late Winter I probably can't avoid feed almost exclusively from feed bags, but this will reduce it significantly.
I know some people who pick up scraps from restaurants, etc.