It's a mystery! The contents of the case in the movie are never explicitly revealed, leaving it up to the viewers' imagination.
Well, that's a big question mark. The movie intentionally keeps the contents of the case ambiguous, adding to the intrigue and suspense. Maybe it's something valuable, maybe it's something dangerous, but we're not given a clear answer.
The case in Pulp Fiction is one of those unsolved puzzles. The movie doesn't show exactly what's inside, leaving us to speculate. It could be money, jewels, or something even more unexpected and unique.