A 23-year-old Google employee lives in a truck in the company's parking lot and saves 90% of his income

As for food and showers, that's all on Google's campus. He eats breakfast, lunch, and dinner at work, and showers every morning in the corporate gym post-workout.

So few expenses means significant savings: "I'm going for a target of saving about 90% of my after-tax income, and throwing that in student loans and investments," he says.

He graduated with $22,434 worth of student loans, and has paid it down to $16,449 over the course of four months. "As a conservative estimate (and taking bonuses into consideration), I expect to have them paid off within the next six months, saving thousands of dollars over the standard 10-year, or even 20-year plans," he says.

Additionally, saving on rent has allowed him to dine at nice restaurants and enjoy San Francisco more than if he opted for living in an apartment.