For many years I've have a git-ignored ".not-committed" folder in all of my repos for throwing extra anything into. It's been a huge life saver!
i usually do "*ignorethis*", so a file with .ignorethis extension does not strictly have to be under a specific directory, this might save context somewhere. similar approach but yeah, a huge life saver!
You can just add it in a user-level gitignore instead of ignoring it in every repo. See: ~/.config/git/ignore