Today marks the 12th annual World Towel Day – a celebration of Hitchhiker's Guide to the Galaxy author Douglas Adams. Towel Day is traditionally celebrated by carrying but there are also fan-organized events taking place around the world.
Why a towel? Because, as Adams wrote, it's "about the most massively useful thing an interstellar traveler can have." Plus, a towel is an obvious sign that will identify you to your fellow hoopy froods today.
The May 25th date doesn't have any special significance in the Hitchhiker's Trilogy. It just happened to be two weeks after Adams' death, which gave fans some time to plan. This year's date -- 5/25/12 -- is particularly cool, though, because 5+25+12 equals 42, which is the answer to life, the universe and everything.
Don't forget your towel!