I’m going to give you the requisite Eskimo joes and hideaway pizza answer for food in Stillwater. Both close enough to the stadium to walk.
I’d get there early and wander through the tailgates. Go to the student union. Go to heritage hall in Gallagher Iba arena. Go to the spirit walk ... usually about 2:15 before the game. The team walks from the student union to the stadium. There are all kinds of things north of the stadium. They shut down the street. If you’re into adult beverages, spend some time on elm (Eskimo joes) and Washington (the strip). Another place you might want to eat is Coney Island on the strip.
If you want some food recs in Tulsa, let us know. I’m sure more people will add to this.