Legendary investor Warren Buffett is known for his modest lifestyle and frugal habits, despite his immense wealth. In 2007, he revealed in an interview something unique he always keeps in his wallet: a McDonald's gold card that entitles him to free meals in his hometown of Omaha, Nebraska, for the rest of his life.

The card exemplifies his simple living while adding an amusing twist to his persona. "So that's why the Buffett family has Christmas dinner at McDonald's," Buffett said.

Buffett's McDonald's gold card is just one example of his unpretentious approach to wealth. His...