this is prolly old new to some of you. But the guys over at http://www.pocketmod.com/ have a pretty neat yet simple idea. They provide instructions on how to make a little notebook/organizer thing out of 1 piece of paper. It's meant to be an organizer and they provide page templates geared toward that. So why did I post this on an art forum?
Well, you don't have to use any of there templates or print anything out for that matter. Just grab a sheet of paper and following the folding instructions and you have a thin little sketchbook that fits in your pocket. Granted it is only 4"x2.5" (lol) and only has 8 pages. But it's something you can keep in your pocket for days that you don't have a sketchbook with you. And the best part? You can make it out of any quality paper you want.
(edit: It folds flat like a moleskine too!)
(edit again: Here's a picture of one of my pages I did in it. The pencil is for a size reference.)