One of my pet peeves is a "public" bathroom that does not have a hook for bags. I often have to go to the bathroom, and I often carry a bag. I've managed to balance my bag on things, hang it on doorknobs, etc. but was pretty much baffled with how to manage a port-a-potty, "Martin can you hold this?" was as good as it got.
Then one day at The English Pit (an outdoor shooting range in Vancouver, WA) while I was using the facilities, I looked up ... and behold ... there was a hook (and a mirror). I haven't done a lot of research, but I can say that not all port-a-potties have this lovely hook. So far, only Honey Bucket brand ones do.
And so I say, thanks, Honey.