How do people get early access to see the players warm up and possible get autographs prior to the game?
They sell pit passes that allow you to go down into the pit about 2 or 3 hours prior to the show.
Stadiums generally open the gates 2 hours prior to game time, and you can get lucky if a player is in the mood for an autograph. Otherwise, you probably need to participate in the team's fan club like Steelers Unite, which offers weekly contests to fans for on-field access prior to the game. Even with access, autographs on game day don't happen too often.
Get quick answers from Raymond James Stadium staff and past visitors.