There’s several tailgates up closer to the stadium that have buffet style food + bar that you can buy wristbands or passes too. Plenty of people will give you free food/drinks and let you hang out but that’s dependent on your personality and how you feel about gauging those situations and going for it ha
I don’t know where you’re staying but I like hitting up the Market St/Sq area and eating before heading down towards parking garages/tailgates/etc
You can’t really go wrong. As for roaming around, I don’t know the actual laws but just go the solo cup route and you will be fine.