I have a "back up / camp gun" that's designed to be basic, and to work under any circumstance. 30-06 on a Mauser 98 action, miilitary trigger tweaked to be smooth, Bushnell Scopechief 4X scope, Weaver type rings & bases, 19" barrel in a sporterized military stock. At present, no open sights yet, but will fit a set this year. You need a basic, sufficiently powerfull gun with basic sighting options, decent trigger, goes bang every time, in a easy to find caliber. It only fires one load weight, good ol Winchester 180 PP. Reasonably cheap, very effective, not even all that hard on the eyes. Hose it down with Break free once in a while, or wipe with a few drops of whatever is in the crankcase, and off you go.
I always felt the main idea on a back up is that if something goes wrong with your main gun, damage, lose ammo, scope f*cks up, what ever, then you need a good solid basic boom stick to get you through the hunt. Unless you're after big bears, the 06 will answer any question you can come up with. Plus, the KISS principle applies.
Case point, standing in hotel lobby in Saskatoon, hunter up from Nashville for a bear hunt, it's sunday morn, guns showed up, ammo & clothes nowhere to be found, and he's got to hop a charter to camp that afternoon. Only guns he had were both 45-70's. Had I had caught him Saturday, could have found ammo. Sunday, if it ain't in the basic dozen that walmart or Cantire carries, you're SOL. Had he a basic back up, he would have been covered.
This happened last week btw.