re: Driving to Green Bay

11 of us drove from Madison to the Alabama game in Dallas last year, which is almost the same distance. We had enough planned out (stopping in Kansas City for BBQ, checking out the Sooner's stadium) that it ended up being pretty awesome. The highlight was putting a walkie talkie in each van to play 20 Questions, vehicle to vehicle. Of course, that's multiple drivers, all around 30 years old with no kids - your experience may be different.
I couldn't imagine doing that drive in one day, though.