In the movie Pulp Fiction------What is in the briefcase?

The primary point of the glowing suitcase is to give a tribute to "Kiss me Deadly" from the 1950's. In the case, they had uranium which when opened, burned up the person who opened it. I personally have never heard Quentin reveal what is in his case. If he never does, that would leave another clic element to the film. I have heard it speculated that Mr Marsellas Wallace's soul was in the case. Others have said a beautiful work of art studded with jewels.