Revealing mistake: At the start of the chase, the Mercedes slides around a bit, and it is comically obvious that the tire smoke has been poorly painted onto the scene. (00:45:15)
Revealing mistake: In the rink, only a few shots after Natasha Kirilova is introduced, the camera pans across the crowd where Sam and Vincent are sitting and you can see that the upper half of the crowd are all cardboard cutout people.
Revealing mistake: During the final chase scene with the BMW and the Peugeot. Just as they go down into the first tunnel, they cut in front of a car transporter forcing it to brake hard. A car on top of it then flips forward onto the road. If you look at the ramp as the car tips up, you can see a mechanical arm/rod lift it up to make it fall off.
Revealing mistake: In the final chase a car gets spun around and hit by a lorry - the car driver is an obvious dummy.
Revealing mistake: Obvious studio shot when the BMW starts to flip at the end.
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 ★