Fire
A lighter runs out. A flint striker doesn't. I keep both, and I'd tell you to do the same. Fire means warm food, boiled water, and a way to dry out. This collection is the simple, mechanical stuff that works wet and cold and still works in twenty years: ferro rods, flint and steel, waterproof tinder blocks, matches in a sealed can. Nothing here needs a charge. Practice with it in the backyard once so the first time isn't in the dark.
