From http://mnmn.essortment.com/survivalfoods_rcnq.htm

Prickly Pear Cactus: The prickly pear cactus offers year around food and water. The plant, above ground is composed of fat fleshy arms and joints and the fruit is about the size of a lemon and red to pink in color. The fruit can be eaten raw. The seeds can be eaten raw or boiled. The pulp of the joints and arms can be peeled and eaten raw or boiled or sun dried. Remember to remove the spikes first. This plant can sustain you for long periods of time and is loaded with vitamin A, B, B12, and C.