If you don't poison weeds in your back yard, you probably have a good source of food just for the taking. You don't have to plant it or water it or weed it or feed it because "weeds" grow in a habitat that suits them without interference from us.
Of course, a little care without overdoing it will help produce more food.
I'm talking about dandelions, purslane, amaranth, lambsquarter and the like. If you're not sure of what they look like, do some research and find pictures of them. Although the ones I listed are mostly used as greens, they can be used for other things, too.
For instance, dandelions make dandelion "coffee" and dandelion tea, wine, salad material and more. Lambsquarter and amaranth provide grains for cereal and bread and purslane is great pickled or fried like okra.
Getting the most from the ground you have is a way of living like country folk in the middle of the city. If you don't have a back yard, find someone who does, or get a little plain dirt and a few weed seeds and grow your own in the window!