A single heat-reflective emergency blanket in a pocket-sized pack.

The cheapest piece of real safety equipment there is. It weighs almost nothing, costs less than lunch, and on a cold night it is the most valuable thing in the pack.

Hypothermia does not need snow — a wet shirt, a breeze and 50 degrees will do it, and that is the most common way an ordinary bad day outdoors becomes a serious one.

Also works as a ground sheet, a rain cover, a wind break, or a reflector behind a fire to throw heat your way.

Buy several. In practice they are single-use — once unfolded, nobody has ever got one back in the packet.