We just got back last night from our 5-day trip to DC. We drove down from NY (and back) during Sasha's nap time, so that helped her. We also got her one of those doodle toys at TRU and she loved "drawing" on it; we had a lot of stickers, some new and old favorite books for the ride. We got a suite at the hotel, so that when we put Sasha down at night, we could close the doors and hang out, I highly recommend doing that if you can swing it. She napped in the stroller and in the Ergo.
Overall, we really just tried to go with the flow, and she did wonderfully! We walked around and saw quite a bit of the city, visited a few museums and the zoo. She did freak out over the butterfly exhibit in the Natural History museum (they had live butterflies), but won't stop talking about them since then. Overall, it was definitely a fun trip!
Just wanted to share our experiences if anyone was thinking of going.