Compresses javascript and css using YUI-Compressor http://yuilibrary.com/download/yuicompressor/
Use package control http://wbond.net/sublime_packages/package_control and search for YUI Compressor
Make sure you have java installed and that it's on the path. On linux and OSX it's usually added by default, but on windows you need to add it. http://java.com/en/download/help/path.xml
make sure you can run java -v from the terminal / command prompt.
Open a .js or .css file and press F7 or command + b.
The plugin generates a new files with the extension -min.js or -min.css