The mandatory one is GIT. It's too easy at the basic level to not use. Github offers free repos for public code. Bitbucket offers private or public repos for less than 5 users.

After that, it's about productivity. What type of jobs you plan on pursuing, etc.

Some useful tools which you should look into to see if they work for you :

SASS/LESS - CSS preprocessors. These are to help you organize your code, avoid repetition and basically augment CSS with some programmatic features.

Package managers : composer for PHP, npm for node.js, bower for general web. Helps keep code up to date and to manage large project's dependencies. There's others, see which works for you.

Build Tools : grunt, gulp, phing for php. Used to 'build' projects from source. Consolidates tasks at a simple level like minifying js/css. Runs other tools like LESS to generate CSS. Real open ended but that's where you start.