Debbie Colgrove of Sewing.About.com has lots of great free patterns on her site, including one for various sizes of Insulated Water Bottle Totes.

This pattern was quite easy. Jeans legs were too narrow for the 25-ounce tote I wanted to make, so I dug a skirt out of my stash and used one of the panels. I always have quilt batting and elastic on hand, so this project cost me nothing!

I couldn't find a decent compass in my office supplies to make the circles for the bottom, so I went to my scrapbooking supplies and used a circle cutter to make a tagboard template.

I've already taken it on a hike and it works great!