The coated cotton worked wonderfully, and I had plenty of scrap cotton for the exterior that both the boys and the girls can be happy with. Hopefully. One minor problem: the thickness of doubled up cotton and coated-cotton was too much for my little old hand-me-down serger. I know, I know. I'm spoiled even to have one (many thanks again Sarah, it has been well loved). But I had hoped it would be up for a quick zip around the edges to save me the hassle of stitching, trimming, and then zigzagging.
Instead, as you see, I stitched, trimmed, and zigzagged. But it was well worth the extra fifteen minutes. Instructions on the coated cotton say not to machine wash, but I did anyway (cold and delicate, for sure) when one bag got loaded with fruit peelings on its maiden run. I hung it dry though -- that's got to count for something.
Now we'll see if the bags last longer than the kitchen spoons that somehow manage not to make their way home after school. From time to time.