Tailgate question

First game Sunday. We were hoping to hit a bar or the Tundra Tailgate Zone we read about. I see this is open to those without tickets...is it crazy crowded? Also what is the scoop with the Atrium? Is that inside the stadium or accessible from the parking lot. (don't want to get into re entry hassles)

So what's my best bet if I'm not bringing food/beer and I'm looking to buy it.

On game day, the atrium is considered part of the stadium and as such requires a game ticket to enter. There are full concessions available inside and outside the stadium like at any other public event. The tundra thing is one such location in the parking lot. It is basically a large semi-permanent bar.