Sometimes the best hacks are the most simple. Here are two rather useful tricks that require nothing more than a piece of paper and maybe a pair of scissors:
The Paper CD case, as the name implies is a simple case for a CD (or DVD or whatever) that is really useful for all those times you burn a CD (or DVD or whatever) and then can't find the stack of empty jewel cases or envelopes sitting around. Just takes a few folds and works really well. The online tool lets you create a PDF file that has tracks or other labels pre-printed on the case. Tom Hull also has instructions for folding a blank sheet of paper without any labeling.
Next up might be an excellent solution to a common problem. Despite several pieces of technology I carry around, nothing beats a pad of paper for quick notes. The problem is I have roughly a million pads around the office and never have the same one handy twice. (ok, I'm exaggerating, I only have roughly 750,000 paper pads) The PocketMod is a flash-based application that prints out a template for a small notepad on a standard piece of paper. Each notepad has up to 8 pages, and each page can have a different template (i.e. to-do, calendar, notes, storyboard, etc) Its really handy, fits in your pocket, and is a great way to keep organized. I use one per week and then archive anything important into my Backpack and thus far this method has worked great for me.