I was going to suggest fusible fleece, then read all the other replies, with some great recommendations. Sewing with Nancy had a series on making all types of bags and totes, and she recommended using cotton duck, which is fairly inexpensive. I also bought plastic canvas to make some totes, as the ones I had made previously didn't stand up the way I wanted them to, plus I wanted to use something in the bottom of the bag that didn't have to be removed when the bag was washed. You got some great ideas here. Next time I've got a problem, I'm coming here for help.