I occasionally use the Git Bash shell in Windows and always miss the ability to tab complete the git commands when in other shells. A couple of days ago I found a bash script that enables this functionality when reading a post on effectively using topic branches in Git by the mozilla web dev team. It enables tab completion as shown below:
$ git sta<tab><tab> stage stash status
I’ve added it to my dotfiles repository on GitHub, or you can access the latest file in the git release tarball at contrib/completion/git-completion.bash.