Zuzu’s petals.
InLikeFynn…You’ll never know.
And I don’t care!
Princess Leia’s breast tape.
Gwyneth Paltrow’s severed head.
Gold lights.
It was Rumple!
The alternate ending to Casablanca.
The head of a famous writer’s wife.
It’s the Colonel’s secret recipe!
Apparently it was just a battery and a couple lights hooked up inside the breifcase to make that light.
Though it could be the Necronomican.
I read somewhere that Tarantino spoke at some convention a few months ago and during the Q&A session afterward, several people in the audience told QT what they thought was in the briefcase. He just smiled and told everyone “Yes, that’s EXACTLY what it is!” or “Whatever you think it was, that’s perfect”.
It’s probably the Golden Apple of Eris, or at least parts of it. As you know, this artifact shows those who see it their heart’s desire, and since there is only one and several viewers, chaos and discord ensue.
He was interviewed on Howard Stern last week, and got this question from a caller. His answer? “whatever you want it be.”
I always assumed it was Uma’s Toenail polish…probably a metallic gold color
HPL wins the cookie. I read a Tarantino interview where he stated “two batteries and a lightbulb”. He followed up with the thought that he had no actual object in mind, just the greatest thing anyone could personally imagine.
~mixie
Although I like the idea of it being Marcellus Wallace’s soul–you know, the bandaid on the back of the neck and all that.
Yeah - I thought the bandaid on the back of the neck had to be there for a reason 
I think it was Tim Roth who gave the “some batteries and a lightbulb” answer tho
JP
The stuff that dreams are made of.
To identify Macellus Washburn.
Look, in the early part of the film, you only see the back of his head. Then, suddenly, Bruce Willis sees Washburn crossing the street. That’s the first time we see his face, and it’s essential to to plot that the audience understand who that man crosssing the street is, otherwise the scene loses all its impact.
So you put a band-aid on the back of Marcellus’s neck. The man crossing the street is instantly identified.
This is so obvious that I keep wondering why people still continue to ask why.