We are still finding new uses for that box of old jeans from my dad. They make great drawstring lunch sacks! My sewing machine is by no means heavy-duty, but it didn’t have any problems sewing through two layers of denim.
I ran the two long seams through the serger, but you can use a zig zag stitch on a regular sewing machine instead. Next, roll the top and bottom hems over 1/2″, then another 1/2″. Pin into place, and top stitch along the edge. This is the casing for the drawstring.