Since the wedding is over Fourth of July weekend, you’ll have the unique opportunity to be in the nation’s Capital for the holiday. Washington DC usually has a Fourth of July Parade on Constitution Avenue Northwest from noonish to 2pm.
The fireworks usually start at around 9pm at the National Monument. We suggest you take the metro (free on the fourth!) to whereever you would like to see them. The monument is visable from Arlington, VA so the website linked here lists some great spots to go if you'd like to stay around Falls Church. We suggest the Iwo Jimo Memorial or Gravelly Point.
The Falls Church city farmers market is every Saturday from 9am to noon. If you’re looking for a taste of the little city, this is the place to go! There is usually live music and a stand that sells the best croissants you’ll ever have.