Despite their ability to spend, spend, spend, even some of the richest people in the world stick to a few frugal habits. For a few billionaires, that means opting out of Michelin-starred restaurants in favor of an American classic: McDonald's. Facebook CEO Mark Zuckerberg was spotted eating a grab-and-go McDonald's meal on the Mignanelli Steps near Piazza Spagna in Rome during his honeymoon with his new wife Priscilla Chan in 2012. Legendary investor Warren Buffett loves the Golden Arches as well. He visits the restaurant every day for breakfast and never spends more than $3.17. On his five-minute drive to the office, which he's been doing for the past 54 years, Buffett stops by McDonald's and orders one of three items.

"I tell my wife, as I shave in the morning, I say, 'Either $2.61, $2.95 or $3.17.' And she puts that amount in the little cup by me here [in the car]," he explains in HBO's documentary, "Becoming Warren Buffett." Each amount corresponds with a different option at McDonald's. For $2.61, he can get two sausage patties, $3.17 gets him a bacon, egg and cheese biscuit and $2.95 buys him a sausage, egg and cheese biscuit. Buffett keeps it frugal even when treating his friends to lunch. In Bill and Melinda Gates' 2017 annual letter, which they addressed to longtime friend Buffett, Bill tells the story of a particularly economical lunch Buffett took him out for years ago.

McDonald's Quarter Pounder hamburger Getty Images