Hand and footwarmers exist.
I wish these people would've taken better care of themselves before going to that game. Players in the coldest game ever, Ice Bowl, along with fans at Lambeau that day suffered lifelong consequences. But that was the 1960s and Lombardi was already at least trying to make things safer; unfortunately, a heating grid installed beneath the playing field malfunctioned. Since then, at least in these traditionally cold regions (Green Bay, Chicago, Buffalo, etc) have passed down tips and tricks over the years. Hand/foot warmers, layers, vaseline on exposed skin, etc. Frostbite is a real thing and it can last a lifetime.
I was at the Green Bay-San Fran playoff game with similar temps a couple years ago and those precautions helped me and many, many others.