MacGuffins

Another clerk, A, is basically a good guy but drives me up a fucking tree with his chronic immaturity. He's a huge sci-fi geek of, to me, the worst kind: the pointless detail cataloger. He's that guy who obsessively points out that, in Predator 2, there's an Alien skull inside the Predator's trophy cage, and that at the end of Cloverfield, if you watch closely you can see a meteor falling from the sky, and that's where the monster came from! Wow-wee! Who fucking cares?
To me, obsessing about that sort of mundane, banal detail is a symptom of crippling literal-mindedness and ultimately lack of imagination. He started talking about his intense curiosity that drives him to need to know, for instance, why the dead start coming back to life in zombie movies. I immediately balked, saying, "Nobody cares why the zombies come back. Radiation, or Indian burial ground, or ancient curse or whathaveyou; all the best zombie movies don't bother to explain why because it's ultimately irelevant. All you need ot know is 'When Hell is full, the Dead will walk the earth'."
I then explained the idea of the MacGuffin a la Hitchcock, the plot device whose detailed explanation is ultimately irelevant to the whole movie. You don't care what's written in the documents the spies are trying to steal; all you care about is how they steal them.
He came back with, "So you don't care what was in Marcelus Wallace's case in Pulp Fiction? It's his soul, you know because there's a bandaid on the back of his neck and blah blah etc."
I would argue that the case in Pulp Fiction is ultimately not a macguffin, because what's in it ultimately affects the way you understand and appreciate the film.
In the first part of the movie, it is a macguffin, because it's contents are not really relevant. The point is, he really wants it back, and they really don't want to give it back to him. It's merely a device that drives the plotty/atmospheric story. Later on, it becomes a fairly clunky and obvious pseudo-metaphor for his soul/innocence/the human element that would stop a normal person from doing these horrible things, etc etc.
My point is just that nitpicking over minor details in movies, which in the end have no importance to the way one reads the movie, is a pointless and dreary exercise. Look at Donnie Darko; all the ambiguity that makes the film so fun and interesting actually has, if you listen to the director's commentary and/or watch the director's cut, a very dry science-fiction--science explanation having to do with God making a time loop that gives Donnie super powers and so on. The abgiguities are actually vagueries.