I was at A2 and I took a small backpack in with me.
Pretty sure the bag and security polices are specific to the stadium and/or the league. It seems as though all the NFL stadiums are on the "clear bag only" policy, at least that was the case with both Santa Clara in 2015 and 2016, and Seattle in 2017 and 2018. Anaheim Stadium has a 16"x16"x8" bag policy but it can be any type of bag. And honestly there were a lot of bags bigger than that going through security last Saturday. So for the OP, double-check the Oakland Stadium security policies and follow those.
And a Monster can gets you pit access as normal, just look for the can drop and stamp spot before you enter the stadium.
Old MXer turned Superfan.