On Making Light, Teresa has written a very sensible document on rolling your own tampons. This strikes me as an eminently practical piece of origami wisdom.
You should now have a strip a bit under two inches wide and about four and a half inches long. If you've done the last three folds correctly, it'll be six sheets thick at one end and twenty-four sheets thick at the other. I find this makes the rolling easier and tidier, but it's not strictly necessary. Once you'd folded the towel lengthwise into halves then thirds, you could just start rolling from one short end to the other; but the strip tends to splay and distort as you roll it. The third and fourth rounds of folding stabilize it a bit.
Starting from the thick edge, roll the strip into a snug but not impenetrably tight cylinder. Use in the normal fashion. It won't be quite as absorptive as the commercial variety, but it's a good deal cheaper and can be improvised at need.
