In accordance with the fact that I'm a huge nerd, I'm going as Arthur Dent (the main character of The Hitchhiker's Guide to the Galaxy for anyone unfortunate enough to have not read the book). I'm basing a lot of it on the disappointing movie version, so it's pajama pants and a bathrobe, my 42 t-shirt and, of course, my towel, as well as my iPhone as my copy of the guide (open to Wikipedia).