However, your suggestions are too scary for me. Over the years, I’ve tried to think of additional alternatives, and I’ve come up with the following:
1) Pay off your house (that’s sort of like your real estate idea, but not really, because it’s really just about only having to pay taxes and insurance to live indoors–it’s speculating that those things will be cheaper than rent)
2) Invest in training yourself in job skills that are in demand
3) Write a book or make another creation that might pay royalties
4) Invest in frugality skills (such as changing your oil) and tools (such as recipes)
5) Stock up on things you know you’ll need that won’t spoil (like your favorite sneakers when they go on sale) (still risky–you could change sizes or preferences, get flooded, etc.)
6) Money under the mattress in small bills and quarters (for natural disasters when ATMs don’t work, for when you need to do laundry at the laundromat, for when you’re eating out with others and want to have exact change)

And of course insurance.

And having good relationships with friends, family, your church, and other community groups could give you access to more resources (for example, ultimate frisbee players house each other at tournaments and SCA members do the same for events; friends might dog-sit or bring you to pick your car up from the shop, etc.)

I wish I knew more ideas.

… if you happen to like the stock market; if you happen to like index funds; if you happen to have a 30 year outlook … then – if 75 years of history is any guide – you are almost certain to average a compund 11% return on your money, and virtually certain (well, as absolutely as investing the day before the Crash of 29, but hanging tight through the crash and the next 30 years) to get at least 8.5% compound.

Hmmm … I wonder what the VIRTUALLY CERTAIN 30 year compound growth rate is on other unleveraged investments?

Of course, if you want to be rich, you’d be looking for leveraged GROWTH + INCOME investments, anyway (stocks on HELOC + margin; real-estate; etc.).