I'm a frequent user of the large shop bag for hauling my kids' stuff around to the pool, ice rink, etc. I don't know if the bag is suppose to be used over the shoulder, but I end up doing it anyway. The problem I have is usually one of the straps falls off and the bag kind of flops open.
Anyway, I ended up using a small key strap from one of my other TB bags to bridge the 2 key rings attachments in the shop bag together. Now the bag doesn't flop open when I don't want it to and I feel more secure about the contents in the shop bag not falling out.
Maybe this is already common knowledge, but it was definitely my "ah-ha" moment of the week.