There are no vaccinations required to enter Cambodia, except coming from an area with high yellow fever risk.
It is definitely advised to have the following vaccinations: typhus, cholera, hepatitis A en B, tetanus and polio. Malaria is a danger when travelling to remote areas and the advice is to take the necessary precautions when travelling off the beaten track. Dengue fever is present, and while not a significant threat proper precautions to avoid mosquito bites should be taken.
Medical supplies are minimal and travel insurance is essential in case of emergency (for example repatriation).
Consult your doctor for recent information and prescriptions.
For smaller issues, Imodium, sun cream protection and mosquito spray, are sufficient.