I guess that depends on what is more important to you, the size or type of the container or the items that you need to have with you.....

I would decide what the PSK will need to do for you and where as well as how you will be carrying it. That will tell you minimum requirements as far as items and it will also tell you maximum size and perhaps the style, shape and qualities of your container.

My thoughts are that a PSK has essentials (knife, signalling, fire, compass, medical and perhaps fishing items) and can be thrown in a big pocket. Anything else goes into my BOB and is easily separated from my PSK or thrown in a pocket if need be.