There are a couple of problems with direct investment in real estate though. It’s expensive to buy even a single property, a minimum of tens of thousands of dollars, and there’s no way most investors can build a portfolio of different property types and in different regions to protect from those risks when you have all your money in just one or two investments.
Wow! What an awesome list! My favorite is the stock photography because I love photography. I have had some success there, particularly with one photo I make some decent income from. I think the key with stock photography is finding a shot that is high demand. Then, find a new unique way to frame that shot. This is the reason my St. Louis Arch photo is a top 10 on both ShutterStock and iStockPhoto. Thanks for the awesome ideas above!
If you're looking to get started in real estate, look at a crowd funding solution like RealtyMogul. It works similar to LendingClub - you commit as little as $5,000 towards a property. When the property is fully funded, you become an owner, and will receive your share of the earnings and appreciation in the property.  Check out RealtyMogul to learn more. 
Udemy is another online learning platform that focuses specifically on courses related to skill building for working professionals. One thing to note about Udemy: The classes we've highlighted are free, but it offers a myriad of other paid options for as little as $10, in some cases. If you have a good experience with a free course, it could be worth a small investment to deepen your skills, too.
If you have specialized knowledge in a certain topic, you can put together an online course to teach others. For example, if you have experience in real estate investing, you can create an online course “Real Estate Investing 101”. The benefit of an online course is that once you create the course material, you can sell it to as many people as you want.
Obviously with such a hugely valuable niche where people will be spending on average around $30,000 to $60,000 on a boat, there will be tons of information and reviews available, right?  Wrong!  In fact, MOST of the boats that I was interested in had zero reviews to be found anywhere on the internet.  Zero.  And all the manufacturers showed was a few pictures, sometimes a sales video, and an abbreviated spec sheet.  That’s it.  I scoured the internet for unbiased reviews of boats and did not find anything helpful at all.