the post by Chris about the spear points out the what the perfect fiream is--the biggest you can carry..
my idea of one is a rifle that you can pack away and forget.
an AR-7 with several box's of ammo in a semi-sealed pack that comes out once a year when the rations and batterys in the kit are swapped out seems the way to go.and here i'm talking survival and not bail out with the idea of living in the hills for the rest of your life--or whatever.