I took some old blue jeans destined for the discard pile and cut strips to make a flexible purse-or-backpack that would be durable for traveling and didn't cost a thing. Because there is no seam at the bottom I have high hopes that it can take some serious wear and tear. (Basically, I made one long rectangle of the strips and then folded it in half and sewed up the sides.) The handle and backpack straps were a thrift store belt that I got for free at one of our thrift store's everything-is-free days.
I love re-imagining trash! There are some more photos on my blog that give a better idea of how I put it together. I hope it inspires you to think of ways to put denim to work for you.