@El OchoCinco thanks for taking the time with that post. I think the two things that scare me most about the rentals: 1) bad tenants and 2) liability. From what I've heard anecdotally, finding a good property manager that you can trust with #1 (or at all) is exceedingly difficult. I get that #2 can largely be addressed with LLCs/insurance, but again, it's the possibility of some disgruntled nut job harassing my family that gives me pause (although I can't say that I've ever heard of this happening...just my paranoia talking). Those hesitations aside, I think adding a few of these is a no-brainer financially.
As far as businesses are concerned, a few HF buddies and I looked at various small businesses a couple years ago and ended up chickening out. Of course, if you go small enough, achieving great returns without much risk is attainable but obviously scaling up isn't feasible. A good example is convenience stores/gas stations. If I recall correctly, in our area, you can recoup your upfront in under two years and the revenue stream is very resilient. But, you really need someone you can trust to manage it and you end up netting about 75k/year if all goes well in a decent location. Putting together a portfolio of these and hiring someone to manage them was an idea that we left on the table.
Another one was AirBnb short term rentals. Great returns, but constant issues. Also, comes with a lot of regulatory risk.