A twenty-inch flexible wire saw with a ring at each end for your fingers.

The cheapest, lightest saw that actually works. It lives in a survival kit, a first aid bag or a jacket pocket and is forgotten until the day it is the only cutting tool present.

It will not out-cut a bow saw or a pocket chainsaw, and it is not meant to. It is meant to be there.

Buy a couple and distribute them — kit, pack, glovebox.