That story about sneaking into the national Championship game brought back memories for me when my roommate and I were able to do the same thing at Ohio Stadium in the 90's for a Buckeye game.
Here's how we did it: My roommates hobby was photography. He spent plenty on gear. He decides that he wants to get on the field for the game to take pictures. Now because of my roommate had a thinning hairline in his early 20's, he looked older than your average college kid, which might have worked in our favor. Regardless, off we go to the stadium wearing "old-guy" wind-breakers, polo's and random arm-bands (we noticed that some of the press folks had arm-bands on at games). We were trying to NOT look like our normal game-day college students. He was holding an absolutely massive pro camera with a huge lens, and I was carrying his camera bag filled with lots of extras, a tripod, etc.
We used our student tickets to get into the stadium well before kick-off, while the teams were warming up. Once inside, We then proceeded straight down to the field. The security stopped us briefly and we just dead-panned him, showed him all the gear and let him know we were there for pictures. I forget exactly what we said. Something like "Yea, we're here to get photos for [some obscure but real newspaper in the state of opponent] and acted like we were pissed to be working on a Saturday. He waved us right in!
We cruised around the field, taking pictures, before finally settling in the corner of the end-zone with the gaggle of other photographers there, taking a knee and even making a bit of small-talk. Whatever they did and acted like, we did.
We stayed there the majority of the game, just acting and taking pics. After halftime, we started getting a bit bored and more adventurous, so we started walking down the sidelines closer to the teams, acting like we belong. Finally a security guard stopped us and asked for our press passes. My buddy turns to me and asks me to get them out of the bag. I rummage through the bag and then exasperatedly tell him, I don't know were they are, I thought I put them in the bag. Of course my roommate starts acting pissed and berating me for being so stupid, and we really thought that this might get the guard to let us stay, feeling bad for the stupid dolt that forgot the passes in the car. No such luck, he said "sorry, no passes on display, you have to get off the field". So we left the field still putting on the show, but as soon as we got off the field we started laughing at how easy it was to get on the field!
Not sure if that would work today, but it's true that if you dress the part, act confident, and don't attract too much attention, you can get into a lot of places!