The best survival tool isn't an object. Know how to do stuff
This is exceptionally true and something that i am trying to do more of rather than stockpiling stuff. The stuff is going to run out... you need to know how to get more. There are some pretty amazing matches out there that will actually like underwater but of course they only do that to prove a point about how waterproof they are. They are also quite expensive. I recall as a scout needing to be able to start a fire only using sticks and brush but I just felt like Tom Hank's character in "Castaway" when I was doing it. Eventually they gave you the badge if you were just able to make smoke to some degree.
As far as guns are concerned I feel as though there is no more versatile a weapon, and easy to use, than a pump-action 12-gauge with staggered rounds.
In a wilderness survival situation, I would consider a .410 single-barrel break action. Light, much lighter ammo, plenty for small game. That said, .22LR is by far the most bang for your buck. Holing up here in bear/cougar/moose country though, 12-gauge buck and ball might be the way to go. Many things to consider depending on your anticipated needs.