Any garden's a chicken garden
... our chickens get a lot of leftovers and scraps from our regular vegetable garden all through the growing season, and they will happily eat almost anything from discarded damaged tomatos to the greens left over from our radish picking.
For winter feed, plant winter squash. Winter squash varieties are typically hard shelled, and will keep well into the winter, hence the name (they aren't named that for being planted in the winter). They are easy to grow, easy to store, and you get a large volume of food for your efforts (though they do need a fair bit of garden space). Just cut a squash in half and put in your chicken run to serve dinner. Also, spinach and kale will grow late into the growing season, and cabbage will grow well into early winter or through it, depending on your climate. You can also grow kale, spinach, cabbage, and carrots under a cold frame with straw for protection.
A lot depends on your climate, though. I live in Maryland, and if we go to the work of tenting our tomatos in the late fall, we can usually plan on picking the last of them shortly before Thanksgiving.
I can't help you on the sunflowers. I've planted whatever I found at the store. It makes for a good treat, but I've never put much work into them, nor have I ever gotten a very good yield.