Once you know the hash of the stash commit you dropped, you can apply it as a stash:

git stash apply $stash_hash

Or, you can create a separate branch for it with

git branch recovered $stash_hash

After that, you can do whatever you want with all the normal tools. When you’re done, just blow the branch away.

Finding the hash

If you have only just popped it and the terminal is still open, you will still have the hash value printed by git stash pop on screen (thanks, Dolda).

Otherwise, you can find it using this for Linux, Unix or Git Bash for Windows:

git fsck --no-reflog | awk '/dangling commit/ {print $3}'

...or using Powershell for Windows:

git fsck --no-reflog | select-string 'dangling commit' | foreach { $_.ToString().Split(" ")[2] }

This will show you all the commits at the tips of your commit graph which are no longer referenced from any branch or tag – every lost commit, including every stash commit you’ve ever created, will be somewhere in that graph.

The easiest way to find the stash commit you want is probably to pass that list to gitk:

gitk --all $( git fsck --no-reflog | awk '/dangling commit/ {print $3}' )

...or see the answer from emragins if using Powershell for Windows.

This will launch a repository browser showing you every single commit in the repository ever, regardless of whether it is reachable or not.

You can replace gitk there with something like git log --graph --oneline --decorate if you prefer a nice graph on the console over a separate GUI app.

To spot stash commits, look for commit messages of this form:

        WIP on somebranch: commithash Some old commit message

Note: The commit message will only be in this form (starting with "WIP on") if you did not supply a message when you did git stash.

Another way to make a directory stay (almost) empty (in the repository) is to create a .gitignore file inside that directory that contains these four lines:

# Ignore everything in this directory
*
# Except this file
!.gitignore

Then you don't have to get the order right the way that you have to do in m104's solution.

This also gives the benefit that files in that directory won't show up as "untracked" when you do a git status.

Making @GreenAsJade's comment persistent:

I think it's worth noting that this solution does precisely what the question asked for, but is not perhaps what many people looking at this question will have been looking for. This solution guarantees that the directory remains empty. It says "I truly never want files checked in here". As opposed to "I don't have any files to check in here, yet, but I need the directory here, files may be coming later".