If I had 30 seconds to grab ONE gun, and jump in a spaceship leaving earth before some global catastrophe,...I'd grab my Ruger MKII target. I'd cry outloud a LOT mind you all the way to Saturn, but that one pistol and a brick of 500 would get me by for awhile until I found a deal on a photon revolver!
Now that I've scared myself that this might happen, I'm going to pack a duffle with my 1911, Marlin Camp45, Mini14, 4"629, MkII and all the ammo and clips I can stuff in there. With some socks,drawers, and a tooth brush.