Vegan is tougher than vegetarian where you do not mind honey, cheese and eggs for example.
They carry Lays chips some of which are vegetarian.
There are carts selling fruit and veggies and trail mix plus Fruitibu all fruit leather like a roll up.
Bengal Barbecue
Outback Vegetable Skewer - Skewered Fresh Vegetables $3.49
You can ask for the following with no bacon:
Safari Skewer - Bacon Wrapped Asparagus $3.79
Dole Whips are not vegan due to the cassein but are considered vegetarian.
Cafe Orleans have the following:
French Onion Soup - Sauteed sweet-onion medley in a traditional broth with melted Gruyere cheese Cup $3.99
Pommes Frites - Traditional French-fried potatoes tossed with Parmesan cheese, garlic and parsley, served with a Cajun spice remoulade $4.99
Creole Ratatouille - A N'awlins twist on a French favorite! Savory vegetable ragout, with tomato, eggplant, red onion, bell pepper, squash, zucchini, and fresh garlic - seasoned to perfection and served with corn cakes topped with grana padano cheese. $13.99
If you do not mind cheese then you have to try Carnation Cafe's loaded baked potato soup.
Vegetarian Gumbo is sold behind the entrance to Pirates and over at the wharf at DCA is a cafe with some vegetarian chili but bring the rolaids, lol.
Wine Conuntry Tratoria offers
Roasted Vegetable Lasagna - Roasted zucchini, red bell peppers, eggplant, layers of tender pasta, Italian cheeses with a basil garlic marinara sauce $12.79
Caprese Sandwich - Fresh Mozzarella, Roma tomatoes, red bell peppers, marinated artichokes, olives and capers drizzled with red wine vinaigrette on savory pretzel bread. $9.99