It's not hard to make a denim rag quilt. I made a denim/flannel rag quilt last year for my nephew's half brother. I did not use any type of batting - the denim makes it heavy enough. I kept the flannel (and fringe) to the front and the denim to the back. Layer a flannel square on top of a denim square, right sides OUT. Then sew an "X" on the square to keep the layers together. If you wanted, you could sew anything in the square, but an "X" is the easiest. Watch out for seams - I accidentally left a few seams in the denim squares and they were hard to sew over. Word of warning - make sure you have good tools. It's a pain to cut the fringe, but if you've got good scissors or snips it's not too bad - just time consuming. I had better luck with scissors than the spring-loaded snips, but I know many people prefer the snips. Also, plan on spending a few hours (and dollars :-)) at the laundry mat to "fluff" the fringe because a lot of lint is produced and could hurt your washer/drier. I put one quarter in the dryer at a time and emptied the lint trap each quarter. Just take a book or some handwork with you.
But like a prior poster said, if the jeans don't have special meaning and you're not into making a rag quilt, it's okay to pass them onto Goodwill.