I think a CO2 pellet pistol is a terrible choice. CO2 cartridges are clunky to have to carry around and keep track of in a survival situation. Once they're gone, your pistol is a club. If it just absolutely has to be a pellet gun, and just absolutely has to be a pistol, then a pump like the 1377 is the way to go.
http://www.pyramydair.com/p/crosman-1377-pump-pistol.shtml

A .22 rimfire is a much better choice. Pistol still wouldn't be my first, but there are a few around the $200 mark that can be found. Browning Buckmarks are numerous, can be found used, and are hellishly accurate and durable. Read some reviews.

An idea for a simple, light, and small rifle would be a youth .22, like a Crickett or Chipmunk. Small and light enough that you could stash it in most backpacks fairly easily. And you would have the benefit of an "easy to shoot accurately" rifle. (I even saw one one time that someone had cut the stock and artfully attached a folding stock.)

I bought my son a Henry Mini Bolt (kind of a Cadillac of single shot youth .22s at $200 + tax) a few months ago. We're both having a blast with it, already more than 250 cheap .22lr thru it. Just a fun, tiny, lightweight gun. It slips into the hydration pouch of one of my backpacks with about 4" of barrel sticking out.

You have a veerrry wide selection of .22 power levels: from CCI Velocitors (have the power to take deer with proper shot placement) to 20gr Colibri. I bought a brick of the Colibri and have already put a couple of boxes thru the Mini Bolt. Super quiet, the loudest noise is the bullet hitting the target. It really is like shooting a good airgun, only quieter (quieter than a CO2 pellet pistol), and with the wallop of a 20 grain bullet - good for up to squirrel. CCI CB Longs up the power and bullet weight a little - good up to feral cat (we used to have a feral cat problem, but no longer, and I mostly used CB longs.) A couple of boxes of mixed power types weigh little and will give you a wide range of humane kills. I really think it's the way to go. Look at a good selection of .22 on ammotogo.com.
Colibri ammo:
http://www.ammunitiontogo.com/product_in...mmo-solid-point

Just my $2 and .02 cents.

lukus