There are lots of good suggestions in the above posts, though of course some of them contradict the others. For my own two cents I have to agree that a .22 rifle is the true "survival" rifle if you had to have just one.

Personally I prefer Marlins, and I keep an old-style wood-blued Marlin Papoose in its nylon carry case with a couple of extra factory magazines and a couple of boxes of CCI Stinger ammo. Light, discreet, perfect for small-game hunting and nasty enough to give two-legged predators pause.

I would also second the H&R/NEF Handi-Rifles if you need something in a larger caliber. Unfortunately they don't make one in 7.62x39mm as far as know (a case of cheap Russian ammo that gets used fast by and SKS or AK on the range lasts a looong time in single-shot). They do make models in all the calibers mentioned above and many more.

You haven't mentioned any military surplus rifles out there, but there are number that come to mind as perfect inexpensive hunting weapons that are also fine self-defense tools. The Mosin-Nagant carbines come to mind as they are cheap and rugged and surplus and commercial 7.62x54R ammo is easy to find. They are just fine as is (the M44 has an integral bayonet, the M38 and M59 never had them). The carbines are getting harder to find, but the long M91/30 rifles are still plentiful and you or any gunsmith can turn a $100 surplus rifle into a lighter, more accurate sporter.

Good luck and let us know what you decide.

Cheers,

Matthew