Awhile back, maybe a year or so, someone posted a how to on another site on making a small rucksack from a pair of denims. If I am remembering correctly, the legs were used as the shoulder straps and were sewn into the waste of the jeans and a rope, twine or other cordage run through the belt loops and pulled tight to close the opening. It wouldn't hold much, but it would work in a pinch.