That's a good question. I started wondering similar thoughts. I've wanted to do pumpkins and watermelon, for a 'just because' reasoning. Then my neighbor started growing some green peppers and gave me some, and damn were they good. So i decided I wanted to do that, lettuce, and other things that I use often that I can't justify going to a grocery store for. My wife really doesn't eat green stuff, so it would all be for me. We have several gardens scattered throughout the yard, all taken up by flowers, lol... and we actually got rid of two because it was making mowing hard, and both had a rotted out wood around em.
This is in our front yard, so i wouldn't plant there, but i'd assume something this size, maybe half, would do you good. If you can dedicate it to 'food' anyway.