Real estate investment trusts (REITs) are another passive investment option for investors who aren't interested in dealing with the day-to-day burden of managing a property. One of the main advantages of a REIT is that they pay out 90% of their taxable income as dividends to investors. There is a downside, however, since dividends are taxed as ordinary income. That may be problematic for an investor who's in higher a tax bracket.
I have only dabbled in drop-shipping before when I had an eCommerce platform 6 years ago or so. I think it is something that you could do on the side, but you would want to do in depth research on the industry you want to get into before setting up shop. It may be a little less passive up front, but over time you could take your hands off the wheel.