Run this from the branch where you want the file to end up:

git checkout otherbranch myfile.txt

General formulas:

git checkout <commit_hash> <relative_path_to_file_or_dir>
git checkout <remote_name>/<branch_name> <file_or_dir>

Some notes (from comments):

  • Using the commit hash you can pull files from any commit
  • This works for files and directories
  • overwrites the file myfile.txt and mydir
  • Wildcards don't work, but relative paths do
  • Multiple paths can be specified

an alternative:

git show commit_id:path/to/file > path/to/file