Graham Stephan can afford to buy nearly anything he wants: The 29-year-old earns up to $220,000 in a single month and is on track to make a minimum of $1.6 million in 2019.

Still, the YouTube star and real estate investor is careful with his cash. "I've always enjoyed the aspect of not spending money, even as a kid," he tells CNBC Make It, adding, "I end up saving about 99% of my income, just because my income is so high, and I keep my expenses so low."

Stephan, whose net worth crossed $1 million for the first time at 26, keeps his costs down partly by refusing to spend on two things: "Number one is coffee. I think the markup of coffee at Starbucks and Coffee Bean and a lot of those places out there is absolutely ridiculous, so I just make it at home for 20 cents."

He buys his coffee at Smart & Final, where he can get a large bag for "like half the price" of other grocery stores, he says.