I would take a lever action marlin rifle in .357 magnum, and a .357 magnum revolver, either colt or S&W.
The reasoning behind this one is that if it ever came down to only having two guns, somethings gone majorly wrong in this country and I probably wouldn't be able to find parts or exotic calibers. Lever action rifles and double action revolvers are pretty much bulletproof. Generally they don't break and they don't jam and they are well built. All of these are qualities you want if you can only have two guns with no chance of replacement or repair. If maintained well you could get unlimited use out of them.
Ammo for .357 is easy to find, especially factoring in .38 special. They are easy to load, and ammo runs the full range from the lightest .38 specials to the hottest .357 magnums, so it would be able to fulfill any task.