Congrats on your future first experience!
Are you going alone or with people?? If you are going with people, how comfortable are you with them, and how well do they know you??
Sunglasses!
May sound comical. They will help with the sun obviously...but more importantly will hide the nervous look in your eyes others may pick up on. Also hides the "pee eyes" ( the look you have when satisfying the urge to pee ).
Wear looser pants or shorts and a longer shirt that is weather and temperature appropriate.
A small bag, whether a backpack or shoulder bag. Put an extra diaper or 2 in it, an extra pair of pants or shorts in case you do happen to leak, as well as a couple drinks and some snacks. If anyone asks about carry-in food, say you are hypoglycemic and need to eat something specific for medical purposes.
If I think of other things before Saturday, I'll post them here.