If it is truly for survival you need a gun that you can have plenty of ammunition for. I would think a .22 under a 12 would be ideal. You can carry a lot of ammo and still have a 12 for really big and dangerous animals.

A lot of Deer get killed with a .22 with a lung shot. I daresay you could kill a buffalo or even a Moose with one if the bullet was proper and well placed.