The Importance of a Towel, from the Hitchhiker's Guide to the Galaxy -

The stylish versatility of our Turkish towels is really out of this world. Don't leave the Galaxy with out yours ;)

The importance of the towel was introduced in The Hitchhiker's Guide to the Galaxy original radio series in 1978. The follow-up book explained the importance of towels in The Hitchhiker's Guide to the Galaxy universe in Chapter 3, using much of the same wording as the original radio series:

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 — daft as a brush, but very very ravenous); 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.