Actually, they did start out as a complete pair of jeans. You can see the ragged edge of the hole at the bottom of the top half, left leg. I've already unraveled the seams, which goes quickly once you find the correct end of the thread to pull.
The waist bag has handles made from cotton webbing meant to be used for the seats of Shaker-style chairs. The Shaker Workshop, in Arlington, MA, sells short lengths of webbing at a discount. It's not enough to make a chair, but it's just right for the straps on yoga mat bags, which I used to make in quantity.
The leg bag's handles are a composite of pink camouflage and purple swirls.