Your laptop has an optical drive that you use very rare or is broken?
Simple: just follow these steps and you can add an extra hdd to your laptop replacing your optical drive!
Step 1: Find a Broken Sata Optical Drive
Be sure to remove everything from it and leave it just with the sata socket.
Step 2: The Soldering Part
Then, using a soldering iron solder the wires to the socket. Be sure to consult the pinout of the slim sata socket and make sure you solder the wires correctly.
Optional, if you have a plastic glue-gun you could use that to make the whole thing more secure.