
Visible crew/equipment: When Vincent and Sam are running through the ice rink's changing rooms to get the case off Gregor, the camera passes a mirror. If you pay attention, you can quite clearly see the boom operator wearing a blue and white checked shirt in it. (01:43:40)
Answer: There's no way of knowing what was in the case. It is a plot device called a "MacGuffin," a term coined by director Alfred Hitchcock. It doesn't actually matter what the object is but is just something that drives the story. It can be any type of object or device such as a "secret formula," "enemy war plans," a "nuclear weapon," a "treasure map," and so on that the characters are either searching for or protecting. There was never any intention to reveal what it was. Its purpose is to motivate the characters' actions and tell the story. Most likely it was intended to be a McGuffin just to keep the audience guessing and thinking about the movie long after it ends.
raywest ★