As others have said, for pre-game, find a bar with a shuttle to the game. As a 21 year-old who intends to have a few drinks, I think your best bet is to pre-game at one of the downtown East Grand Forks bars like Whiteys. The bus will take you back downtown after the game and you will be in walking distance to all of the college-age bars in downtown Grand Forks. And if you stay downtown at the Guest House (f/k/a Best Western Town House) then you won't have to take any cabs during your drinking/hockey excursion. Cabs are not always the easiest to get in Grand Forks, especially around bar close.
As others have said, you must hit the Red Pepper at some point during your stay. You should go to the older one close to downtown. It has more history and better atmosphere than the newer one.
GuestHouse Int'l (formerly Best Western Town House)
710 1st Avenue North
Grand Forks, ND 58203
Phone: (701) 746-5411
FAX: (701) 746-1407