Vault101 said:
...The bandage[footnote]"Band-Aid" is a brand name[/footnote] on Marcellus Wallace's neck and the theory that that's where they took out his soul which is what is in the breifcase.
I don't see why a robber would be interested in his soul, or even know what it is.
I always assumed it was gold, given how it shined just like your run-of-the-mill Aztec golden idol does in Indiana Jones or what have you.
Either way, Tarantino never specified what was in there, and a co-writer of Pulp, Roger Avery, has stated that originally there were no orange-ish glow, and that he in fact regretted the idea of installing a lightbulb in the case, because it gave the whole thing a "supernatural" feeling, which apparently wasn't his intention.
Bottom line, we're kinda supposed to imagine it for ourselves. No prop master can beat the human imagination.