The Hitchhiker's Guide to the Galaxy: The Towel

Just about the most massively useful thing any interstellar Hitchhiker can carry. For one thing it has great practical value:

1. You can wrap it around you for warmth on the cold moons of Jaglan Beta;
   
2. sunbathe on it on the marble beaches of Santraginus Five;
3. huddle beneath it for protection from the Arcturan Megagnats as you sleep beneath the stars of Kakrafoon;
4. use it to sail a mini raft down the slow heavy river Moth;
5. wet it for use in hand to hand combat;
6. wrap it round your head to avoid the gaze of the Ravenous Bugblatter Beast of Traal, which is such a mind bogglingly stupid animal, it assumes that if you can't see him, he can't see you;
7. and even dry yourself off with it if it still seems clean enough.