Superskin large adhesive bandages — ten 2 x 4 inch pads.

Every first aid kit is well supplied with small bandages and short on large ones, which is backwards: the small ones cover injuries you could ignore, and the large ones cover the injuries that actually need covering.

A 2 x 4 inch pad handles a scraped forearm, a gouged shin or a burn on the back of a hand — the ordinary camp injuries that a finger-sized plaster will not reach across.

Ten dollars to stop the one gap that every kit has. Buy a pack and drop it into whatever kit you already own.