Maybe this exists and I just haven't found it, but a way to crumple up notes and throw them out would be really useful... I don't want to litter but I'm not sure what else to do with used notes.
Or on a more personal note, a scrapbook that could house notes that you want to preserve. I have a couple that I received that I just couldn't throw away, but leaving them on the floor of my house isn't much better.