For DC, one thing I'm reminded of is how much DC Locals assume that Museums are free unless they are focused and obviously private(Spy, Newseum, Children's) . It wasn't the tourists who objected to the "pay if you want" little machines inside the entrances of the major Smithsonian Museums, it was the locals.
For food, if you hit the areas up north of the Mall toward Howard, I'd suggest Ben's Chili Bowl. Not off the beaten path, but worth it anyway.
