Although renting out your room or home can also be a side hustle to make extra cash, it's also a great source of passive income. However, another route to go is to get an income property just for the purpose of renting it out. This is even better if you live in a touristy area, because you can probably make even more than usual during the high tourist seasons.
People's lives these days are so fast paced that multitasking has become the need of the hour. That explains why podcasts have suddenly become so popular; they allow people to get information or entertainment while they're in the middle of commuting, working out, cooking, or something else. Podcasts are easier to create than YouTube videos and can be shared just as easily on iTunes. Just select a topic that you're well-informed or passionate about, and start a podcast around it, it's that simple.
Nobody gets early FI investing in bonds, CD’s, or even stocks unless they make a huge income or are extremely frugal or a combination of both. Paper assets just don’t provide enough returns. Business income can be great but it is typically not as semi-passive as I would like and there is a relatively high failure rate. That is if you can monetize an ideal to begin with. RE investing needs to be higher ranked IMO as a way that the “average guy” can become FI.
In focusing on your wealth management goals, investment income is obviously critical but you might fund your goals from wider sources of income.  A typical long-term portfolio might produce about half its return as income and the other half as capital growth, though in times of duress the capital growth component wanes.  In this low-interest rate climate, some sources of income have become quite expensive and may prove disappointing against your spending needs.  But by tax efficiently and sustainably drawing income from wider sources, you might meet your goals while more prudently balancing risk against reward.