When I was there (2001-2005), the campus had a contract w/ Coca Cola where all the vending machines on campus were Coke products only - only exception was that there were Gatorade machines everywhere.
Go Gators!
Go Gators!
Note that that no doubt will include the products of the companies that now have the monopoly.
Coke Pepsi Diet Coke Diet Pepsi
etc
If you deal in any kind of bulk good, you will typically sign a contract with your distributor with some sort of terms.