There are many theories about what might be in the briefcase in Pulp Fiction, but the truth is that the creators of the movie left it intentionally vague and mysterious. One of the most prolific theories out there is the idea that the briefcase contained the soul of Marsellus Wallace.
The theory arose out of an email that got out on the internet from someone who claimed to have had a conversation about this with Quentin Tarantino. The theory states that the first time the viewers sees Marsellus Wallace he has a bandage on the back of his head where is soul was removed and placed in the briefcase.
There are many theories to that. From being a MacGuffin to Elvis's gold suit, the theories are kind of outrageous. There is even a theory that it contains Marcellus Wallace's soul which he's trying to get back from the devil.
I'll tell you all that I know.
The simplest is that it's a MacGuffin. If you don't know that is, it's just something to drive the plot forward. It's nothing and is of no significance to the movie which is kinda true by the way.
The most popular theory is that it contains gold bars since everyone acts surprised seeing it and it has that golden glow. But it's not real enough.
My favorite theory is that it contains an Oscar that Wallace wants to retrieve it for his wife, an unsuccessful actress.It was originally going to have diamonds according to the writers but Tarantino didn't want it since he used it as a plot device in Reservoir Dogs.
That's all the theories I know. Feel free to add peeps