A few weeks before the giveaway, a man walked into the McDonald’s on upper Main Street in Haverhill, Massachusetts, handed the cashier on duty a wad of cash, and said little more than that he wanted to pay for everyone’s meals until the money ran out. Then he left. Nobody got his name. The staff started using the money right away, then thought better of it and called the franchise owner. Christine Yee, who runs the restaurant with her father Dav…