Here are my 10 favorite "Roadfood"-type places in the DC area (in no particular order):
Cameron’s Seafood Market – a very good place to get fresh, raw or cooked seafood at a relative bargain.
Full Kee – Chinese. Excellent meal-in-a-bowl soups and roasted meats.
Ben’s Chili Bowl – Very good chili-dogs, -burgers and -half smokes. http://www.benschilibowl.com/
Mixtec – Mexican. Great tortas (Mexican subs).
C.F. Folks – Lunch only. Delicious and varied daily specials, including (in season) a very good, and bargain priced, crabcake sandwich. http://www.cffolksrestaurant.com
Pizzeria Paradiso – The best pizza that I’ve found in DC.
Ollie’s Trolley – Used to be part of a national chain of burger joints, but they are now independently owned and operated. The ‘burgers are big and look good, but, eating very little beef, I must admit that I haven’t tried one. This place gets recommended because of their "trolley" decor and their surprisingly good crabcake sandwich platter, which consists of a very good crabcake, decent fries and a dollop of cole slaw, for 5 or 6 dollars.
Bethesda Crab House – Assemble a mound of steamed, well-seasoned blue crabs, a paper-covered table, a wooden mallet, some ears of fresh corn, a cold brew and some good friends, and you have the quintessential Chesapeake Bay-area dining experience.
Jerry’s Seafood Restaurant – Expensive, but if the comparably-priced Crisfield’s qualifies as roadfood (see the Sterns’ review), so does Jerry’s, which I think is better. Crab is the thing to order here, in any of its incarnations (cakes, imperial, soup, bisque, "Bomb," "Baby Bomb"). http://www.jerrys-seafood.com
Chinatown Express – The chef standing in the front window making noodles lets you know what to order here. The noodle-based dishes and the dumplings are very good. Especially noteworthy are the Shanghai soup dumplings, which are dumplings filled with pork and broth. They are referred to simply on the menu as pork dumplings (8) and make a great lunch.