Miscellaneous things to not miss:
See White Ford Bronco Recommended by Elizabeth Pedraja
"Things Worth Waking Up For" - new, unusual things to try that only occur or have "that feel" early in the mornings - e.g. birding walks at Dyke Marsh/Rock Creek Park, photography, Captain America's running path
"Use your turn signals and don’t litter your Wendy’s trash out your car window." Recommended by Zack Baumel
Friday night market at SW waterfront metro although they have a website it’s not very popular yet.
Also it’s not in DC but we have one of the best car shows in the world, every Saturday morning (like 7-8am early) at old brogue in great falls.