Another quicker way is:
git stash save --keep-index --include-untracked
You don't need to include --include-untracked if you don't want to be thorough about it.
After that, you can drop that stash with a git stash drop command if you like.
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It seems like the complete solution is:
git clean -df
git checkout -- .
git clean removes all untracked files (warning: while it won't delete ignored files mentioned directly in .gitignore, it may delete ignored files residing in folders) and git checkout clears all unstaged changes.
