Stage all your files you need to stash.
git stash --keep-index
This command will create a stash with all of your changes (staged and unstaged),
but will leave the staged changes in your working directory (still in state staged).
git stash save "good stash"
Now your "good stash" has only staged files.
Now if you need unstaged files before stash,
simply apply first stash (the one created with --keep-index) and now you can remove files you stashed to "good stash".