If you're looking to score drugs, I advise against it. Drugs like Percocet, OxyContin, and other highly sought after drugs are government issued and counted. They need to be special ordered, and the prescriptions that come in are kept separately and looked at every month. Also, all of the pills like that are counted monthly, and if even one or two is missing..it's an ordeal. CII Substances are not something to mess around with.
There's more leeway with Vicodin, Darvocet, Tylenol III, and other things with less narcotic effect.
I was hired at a grocery store to be a cashier, and they needed a pharmacy cashier. I started ringing people, and by the time I left, I was able to type in prescriptions myself for easy things (penicillin, allergy meds). I also filled prescriptions. However, OxyContin and Percocet you will almost always find locked up, and unless the pharmacist trusts you, you can't touch them.