I'm a monster, because while I do make good use of /tmp/ as OP suggests, I also have ~/Temp/, which is ... well, I'll admit it, the kitchen junk drawer of the file system. Screenshots go there, as well as downloads I might want to keep for awhile, camera snapshots, etc.

I consider it important enough that it gets backed up :)

I do this as well. /tmp is for things I know for certain that I only need once. Things I'm fairly sure I'll need again go in the proper directory tree. For everything else, I use ~/temp. That gets included in my backups, and I erase its contents after every backup.