Depends on whether you mean:
what I'd consider to be a true survival type 'thing' (not necessarily a knife) - say where you were to be dropped into a zone for however long and could only take ONE item; OR
the closest thing to an 'all-rounder' type knife for use in the Outdoors, where you were at liberty to take other items along.
The former isn't very likely is it?
In the latter situation, I'd suggest a fixed blade of about 4-5" in length, in a really well-made Kydex/Concealex sheath. You'll turn to that knife more often than anything else, when hunting, fishing, camping etc. The tendency is to think you need more blade length than you really do, incidentally. At the same time though, no one knife will do it all.
I'd suggest a Dozier - Straight Hunter, Pro Guides Knife (my choice), or Wilderness. One of those three, depending on which end (or in the middle) of my notional scale you'd be inclined to be on. In any case, those are serious knives - top of the line. Oh and with a Wilderness sheath (different thing from the knife yes) (not shown on the web-site I think).
http://www.dozierknives.com/