I love the idea of having little intensive eco-systems to feed myself and my family. I love how having different living things can work symbiotically to make less work for me and less waste. Like the nice lady I met this weekend who has her goats, chickens, and vegetable garden all working together.
First, there is something like this Farm in a Box. where the fish provide nutrients to your vegetables and, in return, the vegetables remove extra nitrogen in the water for the fishies.
If you want to take it to the next logical step (gads this is so cool), you can create a Portable Farmwhich basically works on a much larger scale and instead of little goldfish, you also have your very own fish farm and large vegetable garden.