Screens fail — batteries die, phones get wet, signal drops — but paper you can write on in the rain doesn't. A waterproof notebook lets you record the things that matter when it counts: a grid reference, an injured person's symptoms and times, emergency contacts, a route plan, a vehicle registration. Ordinary paper turns to pulp the moment it's wet; waterproof paper keeps your notes legible through downpours and river crossings.
It's a small, analogue backup for critical information in a world that assumes your phone always works. In first aid, navigation and coordinating with others, having a durable written record is more useful than people expect.