Pre-Pay for Their Ham-and-Cheese
Nobody wants to pay for lunch. This is why everybody plans to bring leftovers, but forgets to pack them and then silently yells at themselves as they hand over 6 or 7 or 8 or 10 (ow!) dollars for a sandwich that they could have made at home. On this day, however, you will have snuck into the corporate canteen, or the sandwich truck in the parking lot, and pre-paid for a ham-and-cheese, as well as shown the cashier a photo of your coworker who was dumped by his fiancée, so that when he approaches, castigating himself internally about how he can't afford lunch since neither the wedding venue nor the caterer will refund his deposit, he can enjoy the delight of the cashier saying, "That's taken care of, sir!" Variation: Slip the cashier two extra bucks and have her say, "That's taken care of, you handsome, smart, sandwich-eating devil."