I have never bought into the "one is none, two is one, etc. routine, although if I were in Sales, I might think differently. The one exception I make consistently is the stuff needed to make fire. Typically I will carry a lightweight canister or alcohol stove, as well as all the materials (ignition and tinder) I would use to kindle a campfire. I also tend to go a little heavy on water (I am typically in the desert southwest).

Most of my gear is picked for versatility. It so happens that my very nice, lightweight compass has a mirror, with which I could signal if something happened to my dedicated signal mirror. I usually carry at least some clothing items that are very bright - possible signal application there.

Skill and knowledge are the lightest of all, and can multiply the utility of your gadgets many times over