that just about covers it for Port A! Nothing better than a day on the island, cool wind blowing, sitting on the beach, poles out, sand in your hot dogs, beer in your hand...
One thing you could do, just for a change of pace is go to the water treatment plant. Seriously! There is a boardwalk behind it that goes out into the flats and there are alligators that live back there. Also, UT's marine institute is out there. I know they do tours, but having never done it, I don't know if it is worth it.
http://www.utmsi.utexas.edu/visit/visitors-center.htmlOtherwise, get some beer and some poles and relax. And if you are there on the 5th of September, take in the Larry Joe Taylor show. If not, just buy all his albums and play them the whole time you are in Port A.
If it is real crowded and you want to get away, you have several options. You could take the jetty boat to Saint Joe's island and have the island all to yourself. Go south to Gulf Access Road 2 (I believe it is 2, it is by the water tank). When you hit the beach, go south (right). That takes you to some jetties at Fish Pass. Not a lot of people go there and because it is actually on the state park, you don't need the stupid beach parking permit. Or drive the 40 minutes south to the National Seashore and have 60 miles of beach at your disposal, if you have 4x4.