Not just to be used for drying yourself off, you can use it as a distress signal, to confuse the Ravenous Bugblatter Beast of Traal, or to keep yourself warm as you bound across the cold moons of Jaglan Beta.
So incredibly useful and iconic is the towel that Towel Day has become the annual tribute of the comedic writer, Douglas Adams, who created the Hitchhiker's Guide to the Galaxy trilogy (consisting so far of five novels.)
Since Adams' death in 2001, fans have carried a towel with them on the 25th of May, to show their appreciation for Adams and his work. Blue, red, green, fuzzy, limp, stained, pristine - it doesn't matter what your towel looks like, or how big it is. All that matters is that you take it with you on your adventures. Who knows, it might just come in handy.