I have two PSK's. One is the standard Altoids tin that is always in my pocket any time I am out hiking (I do not carry it around town).

The other is my "backpack-based" kit. That's stored in a standard Nalgene one liter bottle. It's waterproof (because it's a Nalgene bottle!), it holds water (because it's a Nalgene bottle!), I can boil water in the metal cup that slips perfectly over the end of the thing, I can see what's inside (it's translucent), and a bunch of stuff fits inside. StarFlash mirror, full sized compass, etc. If it doesn't fit inside my pack there are all kinds of attachment thingies for Nalgene bottles (neoprene sleeves, etc.) to hook it onto the outside of the pack. This is not a substitute for the Altoids tin kit. It is carried in addition to that for longer hikes with friends, or solo hikes of any distance.