that, in a survival scenario, my one keeper would be the Ben Franklin md 137, in .20cal..
My opinion is that it doesn't weight much or take up much space, it is accurate enough for head shooting game birds for food, powerful enough to take rabbits or other fur bearers at moderate range. .
The reliability of these pump up pistols is in the legendary class, it would not need much in the way of parts or tooling to keep it running for a long time, long enough to get to a better place anyways.
That, and my '06, would pretty much cover it, IMHO...