If you're actually going to be packing this thing a long ways, over rough terrain, you need light, light, light. That means single shot and rules out doubles, pumps, tube mag guns, etc. - too much metal on them. A single shot .410 would actually be perfect - take a few different shotshells and some slug shells for larger game. Or possibly a 28 gauge. Something like the Stoeger backpacker - very small, short and light - lightening cuts on the stock, etc. Or possibly a "Springfield" M6 Scout - can be had in .410/.22lr combo, or .410/.22 hornet combo (didn't know it came in .22 mag...hmm). If you take the large trigger guard off, it folds up nicely. I would think that you DO need one that breaks down or folds up because are you really wanting to carry something in your *hands* the entire time - you may want your hands free to negotiate steep areas, etc. using your hands, and how are you gonna sling the rifle over your backpack even if it has a sling? So that means folding up and putting inside backpack, or strapping to outside of backpack. Marlin papoose .22lr comes to mind if you opt for a .22 over a shotgun.