there are so many things to do, 2 days is not much time but here are my random suggestions.
Check out a list of all the different Smithsonian buildings and other museums and pick whatever fits your interests. Washington DC Museums | washington.org
Catch a show at the Kennedy center if there is anything good while you are in town. http://www.kennedy-center.org/text/calendar/
The Odyssey can be great for ma' and pa' type of thing. I suggest a day time cruise then a show at the close by Kennedy center or a nationals game. there is also a very nice deck-bar/restaurant next door to the dock(perfect place to go before a nationals game) Washington DC Monument Views, Great Dining Entertainment | Odyssey Cruises
National geographic has some nice exhibits and events, depending on what you are interested in. usually it is photographers giving lectures of some kind, but there is other stuff too. National Geographic Events - Washington, D.C.
for food(steak): Ray's the steaks in Arlington is where i had the best meal of my life, Other popular steak houses are "Prime Rib" and Charlie Palmer. All 3 are amazing.