The perfect survival gun is a bit like the perfect survival knife. It doesn't exist. The perfect survival knife would split hairs and cut down mature oak trees with equal aplomb, but it won't happen. So you either compromise and carry a heavy chopping knife and keep it razor sharp, or you carry a small sharp knife and an ax or machete.

Likewise with a survival gun. You can't kill an elephant and a squirrel with the same weapon. At least, not if you want to have anything meaningful left of the mouse. And evidence suggests that guns aren't the best tool for protecting against a bear either. Furthermore, its a bit difficult to eat an entire deer by yourself without a deep freeze. Even if you set out to smoke the meat, you're looking at lots and lots of work to preserve it all. So the compromise I suggest (for most areas, Africa being the only exception I could think of) is to carry a can of bear spray in an easy to reach holster and a .22 pistol. Bear spray for protection against large animals (I doubt moose or cougars would be thrilled by a snout full of bear spray. In a pinch you could even use it against humans, although I'm not certain of the legality of that course of action. And the .22 for hunting and signaling. You can take down individually wrapped single servings of meat up to animals large enough to feed several, if you're skillful. And if you carry 100 rounds of ammo, you can afford to spend some doing the three shots regularly timed in short succession is a distress signal thing and still have enough to feed yourself with out breaking your back with the weight.

The bear spray and .22 pistol is a lighter more compact weapon. The extra weight is pretty small, and its not long and cumbersome to carry. Finally, it has the benefit of being easier to shoot while injured than a long gun. You can fire it one handed or while sitting or leaning in an awkward position.

On the other hand, like a survival knife, a survival gun is the gun you have with you when you're surviving. So if you regularly conceal carry a 9mm or .45 you should starting thinking about what you could hunt with it and how. If you're hunting deer what else can you take with your rifle, what other ammo should you carry to take down different game?