[Will attend my first concert in life] What am I even supposed to do after entering the venue at 12:00 noon?

Because obviously the headliners will be the last to perform and it'll be over by 10:00PM or so. So how do I survive the long hours, especially considering they don't even allow most items to be carried inside the venue?

I have early bird tickets for fanpit, I don't think that offers flexibility in entry time? Because I anyway want to enter the venue as early as possible to pick a spot and stick to it.

Explain like I'm 10, I have zero experience in this.