Just use:
git stash -u
Done. Easy.
If you really care about your stash stack then you can follow with git stash drop. But at that point you're better off using (from Mariusz Nowak):
git checkout -- .
git clean -df
Nonetheless, I like git stash -u the best because it "discards" all tracked and untracked changes in just one command. Yet git checkout -- . only discards tracked changes,
and git clean -df only discards untracked changes... and typing both commands is far too much work :)