There will be rules about things you're not allowed to bring through the security checkpoints.

Here's some information to get you started.

http://dc.about.com/od/specialevents/a/4thofJuly.htm

http://dc.about.com/od/4thofjuly/a/GettingtoMall.htm

Bring plenty of non-alcoholic beverages, and expect it to be hot. Though you're from Florida, so maybe for you it will be cool?

There might be bike valet parking provided by www.waba.org. I don't see it on their website yet.