Git: “Not currently on any branch.” Is there an easy way to get back on a branch, while keeping the changes?

If you have not committed:

git stash
git checkout some-branch
git stash pop

If you have committed and have not changed anything since:

git log --oneline -n1 # this will give you the SHA
git checkout some-branch
git merge ${commit-sha}

If you have committed and then done extra work:

git stash
git log --oneline -n1 # this will give you the SHA
git checkout some-branch
git merge ${commit-sha}
git stash pop