If I am limited to one blade, and one blade only I would have to say a 4" blade with a 5" handle. I can baton, make pretty much anything I need like a spear, get wood for a fire and basic shelter, and I can still use it to dress game. Now, I don't want to think about not having more than one blade though.

Men you can't trust, women you can't trust, beasts you can't trust, but Bussekin steel you can trust