Several years ago we stayed at a Hampton Inn in Arlington for a family D.C. vacation. Hampton offers a decent free breakfast, so that was one meal a day. SInce we were driving, we also brought along a full cooler and tote of food for the room.... bagels, cream cheese, hard-boiled eggs, cheese stick, fruit, pretzels, juice boxes, peanut butter, popcorn, beer, etc (plus plates and paper towels, and some plastic flatware).
We ate Subway and the like during the day while we were out touring (we took the Metro from our hotel). It was pricier than the same would be at home, but bearable (although the lines were long occasionally.... probably because it was a school vacation week).
Most evenings we ate dinner in our room from the cooler. The kids were relatively young and thought this was fun.... especially since we would let them watch tv while eating! One night we had a pizza delivered to the room (we live in a very rural area without any pizza delivery or fast food in town, so this was a novelty!). Then just once or twice during the week we went out to a chain restaurant. It was expensive for what it was, but a nice change, since we rarely eat out.
It wasn't a fancy vacation, but what I like best is that we remember the museums and monuments.... NOT the food! ...................P