There are no VCE prerequisites for post-graduate medicine.
At the University of Melbourne, there are prerequisite undergraduate subjects.
They are 2nd-year anatomy, physiology and biochemistry.
Therefore, the possible subjects are:
Bachelor of Science
Principles of Human Structure (ANAT20006)Human Physiology (PHYS20008)Biochemistry and Molecular Biology (BCMB20002)Bachelor of Biomedicine (these are core subjects within the course so you get no choice but to do them)
Human Structure and Function (BIOM20002)Molecular and Cellular Biomedicine (BIOM20001)And, as you'll find, a Bachelor of Science at Melbourne requires chemistry and methods as a VCE prerequisite.
Therefore, chemistry is a definite must for undergraduate medicine as well as for undergraduate courses that are likely to get you into postgraduate medicine. Methods is required for other undergraduate medical degrees outside Melbourne, as well as for relevant undergraduate pre-med degrees.
Therefore, I would recommend chemistry and methods at the least.