If you provide source code, may it be as an application or as an open source tool, you might want to ship a changelog with it. Using git and gruntjs, makes it easy to create such a changelog fast and automatically.
If you are a developer, you should use some sort of time tracking, especially when you are a freelancer. Tracking your time can help you improve your workflow and calculate realistic proposals.
If you work a lot in the BaSh, you will appreciate the ability to create own preferences and shortcuts. Those will make the terminal an even more powerful tool.
I don't know how I survived before knowing Sublime Text. For me, there is no better editor. It's slim, fast and incredibly adaptable. Not at least because of the thousands of packages available. These ones are my favorites
