How can I easily add weight to a wooden arcade stick case?

From aabyssx: The size of my wooden arcade stick case is medium and it is not heavy. So it is a bit unstable on my lap.
I decided to add some weight to the case and share a very easy way to do it.

Here is what is needed:
- wood screws
- some heavier bolt washers
- a piece of soft paper or cloth
- screwdriver