I believe, when if comes to burger joints, simplicity is best.
IN-N-Out Burger, by far the most popular drive-in restaurant in the state of California, has a menu that is the epitomy of simplicity:
Hamburger
Cheeseburger
Double cheeseburger
French fires (one size only)
Soft drinks (small, medium, large)
Milk shakes (one size only) vanilla, chocolate, or strawberry