La Bottega Nicastro - 64 George St in the Byward Market.
Go for their take-out sandwiches: your choice of fresh breads, deli meats (up to two choices on a sandwich) and vegetable toppings (the spicy eggplant is great). A unbeatable bargain for $5.
Find a nearby bench or park around the market and enjoy. You can't walk and eat with this mammoth.