First let me start with a disclaimer... the following link is a rather long commercial promoting a food survival system.
However, the method is so extraordinary and the cost is so low (currently $37) that I think it would be selfish of me not to pass it on. The system (Aquaponics) promises to provide unlimited food during a crisis even if you have limited space, and it's guaranteed to be so easy to build that even a 12 year old can do it.
If you haven't started prepping or you don't even know what that is, do yourself a favor and watch this video.
Here's the link: http://www.backyardliberty.com/vsl/index_a.php