If you drink a diet soda with a candy bar, they cancel each other out. When eating with someone else, calories dont count if you both eat the same amount.
Foods used for medicinal purpose have no calories.
These include any chocolate used for energy, brandy, cheesecake, and ice cream. Cookie pieces contain no calories, because breakage causes the calories to leak out. If you eat food from someone elses plate, the calories dont count. Movie related snacks are much lower in calories because they are part of the entertainment, and not one's personal fuel.