Invest in ziplock bags to pack and protect. I even pack my underware in ziplock so if they search my luggage, it will be less embarassing.
Make sure to take enough to survive in your carry-on that includes at least a change of underware and all your medications for sure! Please plan your wardrobe around a couple of pairs of comfortable shoes. Airports are no place for heels especially with a baby and remember that you must remove them to go through security.
When I arrive at a hotel for a long stay, I pick up drinks and snacks for the room. I would also advise you to pick up some Woolite and pack clothes that can dry quickly especially since DC is VERY humid. Room service can provide a hairdryer if there is not one in the bathroom already.
I have two tricks that work for me when packing.
One is that I lay out everything I plan to take and then start subtracting what I can live without. I have learned that I can travel (alone) with just a toothbrush if necessary. I really started to re-examine my packing habits when I was traveling around Europe by train. I would look at something and ask myself if I really wanted to haul this all over Europe. In your case, I would treat myself to a taxi to and from the hotel with the luggage.
There are other tricks like learning to roll your clothes to go into the luggage. Remember that flight attendents go for days out of one small roll on bag.
Copy your documents and put the copies in a separate bag and do the same with your money. Might consider getting some Traveler's checks in s
mall denominations like 20's.
If you get there and it turns out that you are really going to use the Metro with the baby, consider purchasing a pass to save money. Might also look into hiring a limo to drive you around to the sights as they can be less money than you expect and lots of fun if you get the right driver. They also tend to save precious vacation time and energy. They can add to your knowledge of the city and cut through the red tape. I swear it's not that expensive and sometimes you can share the cost with another couple.
Finally, I like to take both disposale wipes in one baggie and wet wash clothes in another and still another empty ziplock for disposing of trash. In a humid city the temperature often is warmer that the actual temperatures suggest, so layering clothes for you and the baby might be a good thing.
I also got to the point that I didn't even carry a purse, but only a small camera. There are lots of ways around that. You will probably want a small diaper bag and I carried money and ID either in a tight pants pocket in front or in a elastic purse around my waist or in an elastic leg band like the dealers in Las Vegas.
Inspired? I hope so. Sorry I was short on baby ideas. I might add that if you figure in frequent rest periods for the child you will enjoy your trip more. Stay hydrated too!
Good luck,
C. S.
....Afterthought! Babies seem to suffer from the cabin pressure changes more than adults, so if your baby gets fussy or acts as if something is hurting him badly, please give him some liquid in a bottle immediately and the swallowing will equalize the pressure in his ears.