I'd get a tour of the US Capitol too, it's a pretty impressive building and the visitor's center has a lot of nice stuff in it (of course I'm biased, the wife works there, so I've gotten the "good tour").
Just be sure to bring absolutely nothing with you. They make you throw out everything, including the kitchen sink if you happen to be carrying one, before they'll let you enter. Got a cookie in your bag? Throw it out. Got a bottle of water in your bag? Throw it out.
If you don't want to be hassled, show up with nothing but the clothes on your back, your phone, & a camera.
And it is best to make a reservation for a tour, just be sure to get there at least 45 minutes before your time so as to make it through security.
Indeed, you should hear some of the stories that Amy has to tell.
It really isn't that bad, no food, no drinks, no weapons.
I've done the Capitol Tour pre and post visitor's center and I don't think the tour is anything special anymore. It is much shorter than before, though that could have just been the day I was there. There is a little movie intro and then they take you to one of the old chambers and underneath the dome, then down to the crypt beneath the dome. All told it was maybe 30 minutes. If you are really into the building it might be worth your time, but you can get much the same effect by looking at a picture of the painting around the rotunda and the dome. I can't recall, but I think you can go into the visitor's center without the tour if you want to look around at some of the statues, but even that isn't anything remarkable. I would rank it much lower than the Old Post Office or any of the other museums and such.
Right across the street, the Library of Congress I think is just as interesting and the tours are normally easy to do. I wound up getting a guide who was really into the detail and greatly increased length of the tour, but I think a normal tour is 30-45 minutes and they take you into the central reading room.
If you are hungry and around the area, the National Museum of Native Americans has a good food place that features foods from all over the native areas. It is a bit more expensive than cheap fast food, but not unreasonable. I think a meal with drink and desserts was somewhere in the $10-12 range per person. The rest of the Smithsonian places are Mc Donald's only.
The National Gallery of Art is the only other place with a non Mc D's cafeteria. Food is somewhat limited on the Mall proper. There is a cafeteria in the new Capitol Visitor's center I think, but I didn't look into it to see what it was.
