The Pulp Fiction briefcase is more of a "pure MacGuffin", where the film director / scriptwriters are playing with the concept of MacGuffin more than actually using it as its intended purpose.
After all, its a Tarantino film. He basically expects the audience to be familiar with film theory (or at minimum: expects the audience to already be familiar with "typical plotlines").
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Your typical action movie / popcorn movies: Raiders of the Lost Arc (The Arc of the Covenant), Mission Impossible (The Rabbit's Foot), and Men In Black (Orion's Belt), and pretty much every James Bond movie, has MacGuffins galore and are better examples of it.
The scriptwriter doesn't care about the MacGuffin. But a well written story has the __audience__ care deeply about it. Otherwise, the escalation and conflict has no purpose. Pulp Fiction / Tarantino used the briefcase as an exercise in how to make the audience care for an object, despite never really explaining why that object is the center of all this conflict.
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Golden Fleece, Apples of the Hesperides (aka: Heracle's 11th task), Holy Grail. It doesn't really matter what these objects do, we just use them as storytelling devices to get the characters thrust into conflict.