Hmmm, I also wondered that myself but have never been able to come up with any answer that made sense. I suppose that's what Quentin wanted...to always keep up guessing. It couldn't have been money or Pumpkin wouldn't have looked at it with such reverence. What do you think it was?

Im not so sure either but a rumor i heard was that it had the diamonds from Reservoir Dogs. Another rumor was that the case contained the soul of Marcellus Wallace! Rumor has it he sold his soul to the devil and that its stored in the case, hence the 666 combination and the band aid on the back of marcellus's head (thats where you get your soul sucked out)

Other rumors that i have heard...

The Oscar Quentin hopes to win
The ear of the cop from Reservoir Dogs
The Holy Grail
Val Kilmer's Elvis suit from True Romance (a movie Quentin wrote)

Do any of these sound right?

I have heard the rumor about the holy grail before.

lots of crunchies!!

i believe the whole diamonds from Reservior Dogs theory

er uh ok tarantino fans q. said multiple times that this his most asked question and his reply is always either idk or ill never tell.a few things to remember though...diamonds ears crunchies and elvis suits dont glow like et's finger the holy grail maybe. fact is its just one of those famous unanswered questions that well never know the answer to ( like for example what do you do with the three shells in the bathroom in demolition man) and if we did ever find out an actual answer it would somehow mar the movie for us. ithink maybe it was marcellus's collection of gold teeth taken as collateral or maybe ..........................................­...­...­...­...­...­...­...­...­...­...­...­...­...­...­...­...­...­...­...­...­...­...­...­...­...­...­...­...­...­...­...­...­...­...­...­...­...­...­...­...­...­...­..