Good list of space saving items!
We have that collapsible trash bag holder too!
I use smaller (shorter) bags, so I use less "poles" to make the trash bag holder shorter. We use ours inside the camper.
The key thingie is pretty cool, too. I'll keep an eye out for one of those for sure. The folding step stool looks mighty handy as well.
I hope you don't mind if I add to your post's theme, Handbuilder... here are a couple of more ideas for folks:
We use a bathroom suction cup item (soap holder?) stuck on the microwave door front for Gary's wallet. This way it's kind of tucked around the corner, out of immediate entry eye sight.
We also use suction cup style hooks, for hanging trash bags outside, up off of the ground. He hangs it on the rear roof of the camper. While grilling Gary likes a trash bag outside for things like meat wrappers, sweet corn husks and *ahem* beer cans. This trash bag goes in the dumpster each night when we go to the bath house for our showers.