CIA is trading his anime collection for Dr. Pavel. This collection likely consists primarily of mecha anime, most notably Tengen Toppa Gurren Lagann, as a form of escapism from his smallness.
The briefcase may contain a serum turning the person who uses it into a big guy. This may explain why investigators fell for the ploy with the Cadaver. It is also possible that CIA confused his target with Antonio Diego of Project Gilgamesh fame.
According to one "document" released as part of the ARG for The Dark Knight Rises, it contains $3,000,000. However, when the plane is attacked, paper can be seen flying all around the fuselage, leading to the belief that the case was switched (presumably by Maimen) and that the money inside was fake.