Git diff against a stash

See the most recent stash:

git stash show -p

See an arbitrary stash:

git stash show -p [email protected]{1}

From the git stash manpages:

By default, the command shows the diffstat, but it will accept any format known to git diff (e.g., git stash show -p [email protected]{1} to view the second most recent stash in patch form).