Heritage Plaza downtown is a nice place for photos and a short walk from Titletown pub. The Heritage Trail is a nice walk if you need to stretch your legs, but non-essential. The 1919 Kitchen in the stadium was good the one time I ate there. Reasonably priced and near gastropub.
Get some of the local brews. Like most states, lots of great local beers. Get the Beer Advocate app to help guide you since they will be unfamiliar.
Enjoy the party around the stadium on game day, but hit the pro shop the day before. Better inventory and less crowd. See the Giant Lombardi Trophy. Save some room for game day food and go beyond brats and beer. My seats are next to a Food Network Pac and Cheese stand - brats with mac and cheese. Horsecollar the other way, but some actual cuisine too. Mixed drinks are widely available too. Be aware of the carry in rules, which are pretty tight now. If you don't drink, there is a designated driver program with prizes. Depending upon the weather, the rented seat cushions are a good idea, especially if you have an aisle seat.
If your seats are high up, walk down and get a view. Easiest to do in the end zones. If low, go up and get the birds eye view. I'm in row 14, but my sister is in row 59 and my brother is higher. I always visit them during the game and enjoy the view.
Take lots of photos with more than a phone. With a medium zoom, you can get some great shots during the game.
If drunks are bothering people, don't hestitate to get an usher involved. No reason to let a few jerks ruin the game for people. Some people can't handle their drink and start harassing others.
Stadium tour is worth the time, since there is a lot of the stadium you won't see otherwise. Haven't seen the new HOF, but I will get there eventually. If it wasn't 90 miles away and I was from out of state, that would be a priority.
Take Aaron's advice and R-E-L-A-X. Dally. Tarry. Dawdle. It's a vacation, right?
Yes, I miss Tooner's page. Plus he helped a bunch of us get tickets. He sits in section 103 I think, down in the first 10 rows. Stopped by and saw him once a number of years ago.