As I put it on both sides to make it totally waterproof it made the fabric very stiff (seems like a no-brainer). This meant that I had to add a piece of regular fabric to the top for the drawstring otherwise there was no way it would draw closed.
I made it have a box shape bottom so it would stand up and added some nice long straps so it can be worn as a back-pack. I used loops of strapping at the bottom for the straps to thread through (remember to add them while sewing up the bottom).
Over time the bag has been dragged on the ground a little which has worn some of the vinyl off, but it is on year #2 and doing well.
The other school item I made was a couple of book bags for relatives. They tried the store bought ones but asked for replacements when they fell apart. I think the combination of having two layers, the outside one being a strong drill, means they last a bit longer. I also painted the kids names at the top instead if having a pocket for the name tag as the name pocket got torn off my son's one.