If you need to leave most of the “ten essentials” behind, make sure you keep the Ion on the short list.

This emergency backup headlamp provides you with two SuperBright LEDs for close-range lighting. Stash it in your pocket, keep it in your first-aid kit or throw it in your pack. The Ion is the ultimate light for when you don’t think you’ll need it.
Weighs less than an ounce.