If it was one long gun for survival, hunting, and defense; Hands down the 12 guage. IIRC, the late renowned gunsmith and cartidge designer Frank Barnes once quipped if that he had to chose a single gun to travel the world with it would be the 12 guage. Good enough for me.

Now, if you are going to throw a handgun in the mix I'd go with the .22LR. Pistol or revolver? Your choice. Non-destructive on little critters of the meat variety.

If you need to have a rifle then I belive the .30-06 is the ticket. Caveat, the .308 crowd will call you nuts and say you can take equal game with their darling. This cartidge applies to the Continental U.S. If you are going north of the 49th parallel then the either the .338 Win Mag is probably a better choice. Fierce critters in the arboreal North; Canada and Alaska.

All that to say this: Like IzzyJG99 says - 12 guage. Although I prefer the Ithaca 37.