We usually have about 12-30 heavy breed laying hens around the place. Their summer coop straddles two chicken runs, about 75 x 20' each. I alternate sides every three weeks or so to let whatever wants to grow there recover from being scratched to death. I liked the idea of laying down chicken wire to prevent them turning both places into bare mud. It's not practical for the whole run, though. One side has a small pond, lots of berries, goldenrod, brown-eyed Susans and a wide variety of other plants. The other side includes our compost area. After turning the compost, we often let the chickens harvest worms for a couple hours before we close it up again. (We have four bins made of pallets for turning, aging, etc.) Squashes and tomatoes usually volunteer around the edges of the compost piles, so we try to protect that from the chickens to give them a good snack when everything's ripe (or overripe!) All summer, the chickens get various weeds pulled from the garden, as well as food scraps from the kitchen.
In the fall, I turned them loose into about half of our 2000+ square feet of garden. They did a great job tilling the soil. Not deep enough to disrupt the mycelial highway we have going there, but they got every last weed out of the gardens and went to town on leftover veggie stalks.
In the winter, they scratch around in the hay the sheep reject. Plenty of seeds in there. Seems like they actually eat the hay, itself, too. Recently, we entered into a deal with a local, high-end coffee shop to get their food scraps. There's a nice mix of breads, potatoes, and veggies in there, with a bit of meat, too. The chickens love meat! Throw them the bone from a nice roast, and they'll clean it bare in a few hours. The only meat we don't feed them is chicken.
So, we're already supplementing their store-bought feed quite a bit. I'd like to get off store-bought feed entirely. I'd love to hear from someone who has accomplished that. (We're in Zone 4.)