Back when I was in middle school (mid-90's), I was on the student council, which was responsible for maintaining relationships with the junk food vendors (we used it to raise money for other projects). We switched from Coke to Pepsi during that time, and I remember them coming to us with a deal that involved them providing the vending machines, running some contests, and some other goodies for the school. All we had to do was give them exclusive access.