This is one of my favorite bags. It is called a No Sag bag. Meaning that it is so constructed that it won't sag. I made the bag from denim, which I quilted, then cut the bag pieces. Inside, there is a zippered pocket that is built into the bag itself, that gives the bag the the strength to never sag. It took some bit of sewing to get it done and if I remember correctly, I said I would never make another. But, I like the bag so much, that I am willing to try making it once more. Besides, enough time has passed since making this one, that I have forgotten most of the frustration in the making.
This was a bought pattern called: No Sag Bag from Oregon Treasures. It had a tote bag as well as a diaper bag pattern. I believe the pattern was published in 1983.