I just saw this topic listed on the Manhatten thread and thought it was a great idea. The food item has to be less than $10 but can be from a restaurant/stand/cart etc...doesn't matter.
My top 3:
*Turkey, Bacon, Swiss, Russian Dressing, Lettuce and Onions Sandwich on Pumpernickle bread at So's Your Mom (Adam's Morgan) -About $5
* Tempura Sakana Roll at Sakana (Dupont)- About $3-4
*Cold Sesame Noodles at Mr. Chen's (Woodley Park)- $3.95