These are all examples of bribery. It may not seem like a big problem at first. But these little favors can mean big trouble. Employees frequently associate with vendors or suppliers. Employees receive free tickets for sports events, shows, etc.
Reputable businesses refuse to submit bids.
One person has responsibility for issuing and approving bids. To fight the problem, institute strong policies against accepting gifts, make sure employees require competitive bids, and rotate purchasing agents and suppliers.