What’s the origin of Towel Day?

Douglas Adams , best known as the author of the Hitchhiker’s Guide to the Galaxy , died of a heart attack at age 49 on 11 May 2001. He was cremated in Santa Barbara (USA) and his ashes are buried in London (UK), where a Service of Celebration was held.
His fans wanted to organize some kind of wake in his honor. Because some time was needed to get the word out, Towel Day was organized two weeks after his death, on 25 May 2001. After its initial success it became an annual event.

Extract from the proposal posted in the “Binary Freedom” forum by D Clyde Williamson, on Monday May 14, 2001 06:00am PDT:

Douglas Adams will be missed by his fans worldwide. So that all his fans everywhere can pay tribute to this genius, I propose that two weeks after his passing (May 25, 2001) be marked as “Towel Day”. All Douglas Adams fans are encouraged to carry a towel with them for the day.

Make sure that the towel is conspicous- use it as a talking point to encourage those who have never read the Hitchhiker’s Guide to go pick up a copy. Wrap it around your head, use it as a weapon, soak it in nutrients- whatever you want!

Why celebrate on the 25th of May instead of a more meaningful date?

Many other dates had been proposed. For those with an exceptionally long attention span: the 42nd day of the year (“Happy Adams Day”), 42 days after his death (“Second Day of Remembering”), the 11th of March (his birthday, around which from 2003 on a yearly “Douglas Adams Memorial Lecture” is held), the last Friday of every May, the Friday before the 42nd week-end day of the year (occasionally falls on 25 May, as it did the year he died), etc.
Of all proposed dates, the 25th of May turned out to be the one that gained a significant following.

As the universe that Douglas Adams created was full of absurdity and randomness, it may be a fitting choice after all. And if you need an additional reason: if you add the hexadecimal numbers 25 and 5, and convert the result to decimal, you get 42!

What kind of towel should I carry?

Any towel will do. One is enough, though some fanatics may try to carry 42 towels.

So this is the nth edition of Towel Day?

2011 is the year of the 10th anniversary of Douglas Adams’ death, but of the… 11th Towel Day! The confusion arises from the fact that the first Towel Day occured shortly after Douglas’ death, long before the year of its first anniversary. Maybe this can help:
2001 – Towel Day #1 (year Douglas died)
2002 – Towel Day #2 (Douglas 1 year dead)
2003 – Towel Day #3 (Douglas 2 year dead)
2004 – Towel Day #4 (Douglas 3 year dead)
2005 – Towel Day #5 (Douglas 4 year dead)
2006 – Towel Day #6 (Douglas 5 year dead)
2007 – Towel Day #7 (Douglas 6 year dead)
2008 – Towel Day #8 (Douglas 7 year dead)
2009 – Towel Day #9 (Douglas 8 year dead)
2010 – Towel Day #10 (Douglas 9 year dead)
2011 – Towel Day #11 (Douglas 10 year dead)

The Hitchhiker's Guide to the Galaxy The Restaurant at the End of the Universe So Long, and Thanks for All the Fish
The Hitchhiker’s Guide to the Galaxy The Restaurant at the End of the Universe So Long, and Thanks for All the Fish