Plaza Inn -- Fried chicken plate is probably the best value + flavor proposition in the park, it's a lot of food. Plus it's a great little spot, even better if you know the history of that spot/the original park vendor from 1955. From the menu: "three pieces of Chicken fried to a golden brown and seasoned with distinctive Herbs and Spices, served with Mashed Potatoes, Buttermilk Biscuit and a mixture of Vegetables" $18.49
Jolly Holiday Bakery -- Grilled cheese and tomato soup (aka Jolly Holiday Combo), perfect on a cool fall morning in the park. Pro tip: if you have a picky eater who only eats grilled cheese, they will sell you the sandwich alone (have to order that in person, not available on the app for order ahead). $10.19
GCH Craftsman Grill -- Inside GCH (enter and turn left from the DCA exit into GCH) is this little gem with a delicious burger. From the menu: "8-oz Burger with Grilled Asparagus-Celery Salad, Spiced Hollandaise, Swiss Cheese, and Artichoke Aïoli with choice of French Fries or Fruit." Of the three times I've gone recently, it's usually fairly empty/plenty of seating. $16
*prices as of today, 5/5/2020
EDIT: added links to each menu