So why does it have to be a firearm?

Many places, an air rifle would work, or just a good ole bow with a quiver. Easier to replace broken parts in the woods too.

Personally, in 24 years of camping, I've NEVER carried a firearm into the woods. Absolutely never needed to. I have to agree with Taurus (welcome back, btw), there's a false sense of security with them.

OK, back on-topic. A .22 (I'm partial to a 10/22) probably works best. A buddy of mine had an old bolt-action with a 10-ish round magazine, and that was nice. Slap on a lighter stock (bullpup even?) and you've got a nice solid set up with greater range and only slightly worse weight. Of course, a .17HMR probably would work too.