light sticks in the car. Glad we did - a puncture on a dark lane would normally have left me cursing the flat battery in the torch, calling the AA and flattening the car battery with the hazards. But these glow sticks were (just) enough to see to change the wheel, and mark the offside of the car for passing traffic.
They work when you bend them to crack and inner capsule and mix a couple of chemicals, creating an unstable reaction - basically electrons jump orbit and give off light: a similar idea to fluorescent paint, but turned up to 11. The sticks don't get hot, and were still giving off light 24 hours later. Readily available for pennies on eBay, they'll fit in a glovebox or under a bike seat no problem. Genius - don't leave home without them