Looks like this has turned into a knife thread. I'm going back to the OP's original title, (but include a knife haha).
I took a survival class this past May. It wasn't a military type school but a native american style school and was a week long. It was one of the best experiences of my life. Something that stuck out, among many was the rule that says everything you carry should have a duel purpose... A poncho that doubles as a tarp, a compass that doubles as a reflector to signal and so on.
Another thing learned is cordage can save your life. You can make traps with it, shelter with it, on & on. 50' is good 100' better.
And yes a good knife is all encompassing. Mine has at least five purposes. I can carve with it, like making traps, I can baton with it and I can also lash it to a limb to make a spear, and maybe most importantly it's made of carbon steel so I can use it to start a fire in an emergency. and of course defend myself with it.
And Geronimo, we were asked the first day to list our top five items to carry. None of us had an axe on our list but it was the instructor's #1 item to have. So good choice.
Here is my booshcraft knife...
And if I may be so bold as to give the place a plug. It is called the Midwest Native Skills Institute
http://www.survivalschool.com/