Well, the OLD bag was bustin' at the seams. So I used it as a pattern and stitched up a replacement. This is what we use for our library materials.
The original was a cheap reuseable shopping bag. It measures 15.5 square with an 8 inch side and bottom. I had the heavy-duty fabric on hand as well as a heavy black fabric that I used to fashion the straps. I reinforced the bottom with a second layer of the floral fabric.
The seams are all zig-zagged before binding with bias tape to seal the raw edges. Narrow bias tape is also used to bind the upper raw edge.
A plastic shoe box (sans lid) is dropped into the bottom as further reinforcement and to keep the base from sagging when being used.