I see it often advocated on the main sub to multiply and diversify your income streams, yet rarely have seen advice on how to add more income to your life. Obviously, no RP minded man wants to be exclusively tied to one income stream, particularly a typical 9-5 where you're tied to the success of the company and whims of management.

Any advice on this? Obviously, freelancing is the first that comes to mind, but many companies do not let you do this (mine doesn't). How do you guys diversify your income?