Here are few of bash command to save your time or increase productivity
1. Autocomplete ssh machine names
If you often ssh remote machines, this autocomplete for ssh will work well for you.
How to use? Append this to your bashrc file (~/.bashrc).
2. Git branch name, a permanent member of your shell
3. To find Union, Intersection and difference
4. To update environment variable of a running process
5. To create patch files
EDIT: Here is my complete bashrc