Since I posted last, and it will be awhile again... but! I found an article on how much space it would take to grow food for yourself and your family. And honestly? Not that much. About a 1/4 acre, or 100'x100' plot, for a family of four! Plus, when you consider that you really would likely buy things like soybeans for soy milk, and wheat and dairy... well!
So, while it's not reasonable for me in my city *right now* - now you know!