I was there for that one as well with my oldest. We were good through most of the game, but in the 2nd half it was catching up with us.
I wore:
Boxers, base layer tights, pair of jeans, snowpants.
T-shirt, long sleeve thermal shirt, long sleeve thin shirt, sweathshirt, heavy coat that essentially had an inner layer as well.
Warm insulated boots with foot heat pads activated before walking to the stadium. Make sure they are warm when you put them in. They need air to work. I had two layers of socks on inside insulated boots.
Wore a face gaiter thing to keep face and head warm, then had a ski mask stocking cap I could pull down over my face after that. Had several activated hand warmers in my pockets as well.
That night they had handwarmers handed out in the drink holders of all the seats, but they took about 20-30 minutes to warm up in that cold.
The 2018 Northwestern game was cold but we sat on the sunny side. That made a definite difference, and if there is sun out, Minnesota should take the sunny side for the first time ever.