Some time ago I came across a very useful instructional video on how to survival float. I have been practicing it in pool since then. I find this technique to be much easier then floating on your back - you can see what is going on around you and almost all of your muscles are relaxed. Only your head is moving in order to inhale and exhale.

I once stayed in this position for maybe 15 minutes, then it got a little bit boring . This summer I want to test it for at least 30 minutes, preferably in open water.

http://www.youtube.com/watch?v=kMeierw40nQ