"It's their property; they get to make the rules. While it's true that they cannot search your bags if you do not give "them the authority to do so, and while it's also true that they have no legal right to seize your possessions such as alcohol, they have every right to ask you to drive safely while you're listening to the game on the car radio on your drive home."
Truth is, though, it is OUR property, owned by the citizens of Montana since it is a state school and not a private institution. They can promulgate all the rules and policies they want, but they are not laws and cannot trump a constitutional amendment, one of our ten ordered bills of rights. The fourth amendment protects against "unreasonable searches and seizures unsupported by probable cause and sworn warrant." It would be fun to see a case go to court and be adjudicated. Meanwhile, most of us will continue to bootleg our FireBall or Jaeger in our flasks in for a nip after each GRIZ touchdown! It is part of the game day experience, right?