Steam

"A towel is just about the most massively useful thing an interstellar hitchhiker can carry. Partly because 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 around your head to ward off noxious fumes or avoid the gaze of the Ravenous Bugblatter Beast of Traal (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 you can dry yourself off with it if it still seems to be clean enough."

Also useful when treating yourself to a steam in a bid to clear your clogged up head; I steamed my bonce until I was dizzy for just 25mins of glorious, uncongested schnozz time.