Douglas Adams best known work was the Hitchhiker’s Guide to the Galaxy in which he explained how a towel is the most important item an intergalactic hitchhiker must carry. To honour him, people celebrate Towel Day on May 25.
From Chapter 3:
A towel, it says, is about the most massively useful thing an interstellar hitchhiker can have. Partly it has great practical value. You can wrap it around you for warmth as you bound across the cold moons of Jaglan Beta; you can lie on it on the brilliant marble-sanded beaches of Santraginus V, inhaling the heady sea vapours; you can sleep under it beneath the stars which shine so redly on the desert world of Kakrafoon; use it to sail a miniraft down the slow heavy River Moth; wet it for use in hand-to-hand-combat; wrap it round your head to ward off noxious fumes or avoid the gaze of the Ravenous Bugblatter Beast of Traal (such a mind-bogglingly stupid animal, it assumes that if you can’t see it, it can’t see you); you can wave your towel in emergencies as a distress signal, and of course dry yourself off with it if it still seems to be clean enough.
The other most famous concept from Adams’ series is The Answer to the Ultimate Question of Life, the Universe, and Everything is the number 42.
One item that is a permanent fixture in my saddlebag is a towel.