Things to note, via the MLB press release:
The gates open at 4:00 p.m. Central
On-field ceremonies begin at 6:20 p.m. Central[...]
Do not bring anything that you would not be allowed to bring on a plane.
The rules for what items you can bring into the ballpark will be the same
as TSA restrictions which you can find at www.tsa.gov as gov. Any items
surrendered at the gates will not be returned.