Method to passively bitcoin mine with your PC, doesn't cost anything to set up.
Go to
https://www.nicehash.com/
Go to check your profits
Do auto detection or manually enter your hardware and electricity costs, this will tell you whether it is profitable for you or not.
If it is profitable (mine I can make $2.90 / day after electricity costs) go sign up at "get started".
Once you do this and download the software, you can choose which of your hardware you want to mine with. I recommend GPU mining only, but it is up to you.
Link to a deposit address, and there you have a small passive income running in the background.
I make roughly an extra $80 per month doing this, after fees, which I usually just lose by gambling but it is still nice to get money for doing nothing.