I have a whole stack of my husband's old jeans. They make great bags and are also good to line bags. I made some sling bags several years ago and lined them with jeans. I didn't have to use a lot of interfacing that way and it gives pieced outside a good sturdy lining.
I gave probably 10 pair to a quilter I knew years ago to make jean quilts for her teenagers. She was so happy and said that the kids loved them.