OK, i know that the whole idea is around the suitcase having "Pulp Fiction" in it, but what is it really?

Though it is never answered in the movie what is in the cặp, vali, cặp tài liệu (just knowing that what is in there is valuable and emits some sort of golden glow), there are several theories. One is that the cặp, vali, cặp tài liệu contains the diamonds from "Reservoir Dogs". Another is that the cặp, vali, cặp tài liệu contains Marcellus Wallace's soul. I personally think that Quentin Tarantino left the idea of what's in the cặp, vali, cặp tài liệu for the viewer to guess.

The whole idea behind the suitcase is that it is the most valuable thing that the viewer can think of. Whether bạn want to think it is full of money hoặc the Koh-I-Noor diamond, it's your choice.