Here's a great tip if you run a business and want your employees to start working harder . . . without having to give out raises, God forbid. According to a new survey by Staples, the key to productivity is . . . FREE FOOD. 73% of employees said they'd be happier at work if their office had a well-stocked kitchen.  57% believe that if there was more free food, everyone would be more productive.The survey also estimated that American workers leave the office to get coffee more than 85 million times every year. That's total, not 85 million times per person.  But it leads to 10.6 BILLION HOURS of lost productivity a year.