A very thin knife to add to a PSK is the SAK, Vic Secretary or Wenger Patriot, both are aluminimun sided, 2 bladed folding knives.

I have a Patriot and the closed size is 0.220" thick x 3.345" long x 0.710" wide; the blades are 2.3" and 1.4" long.

While it is not a knife I would baton with, it is definitely more usable than a scalpel blade.

I am at present creating a wallet EDC kit and this thin Patriot is the knife that will go in it.

Mike