Re: Prescription medicines for first aid kit
You won't just be able to buy it at a pharmacy, you'll need to pay for a doctor's visit and then explain to him why you want an rx for narcotics, and many states are getting much tighter about that these days. And the side effects of most heavy meds (Bugs! Get them off me! Bugs!) can be a serious concern as well.
If you have an existing relationship with a doctor, they may be willing to write you an rx for the entire offshore med kit, whatever is within reason. Of course, you may have to pay that without insurance since there's no medical need for it at the time.
And this brings up one advantage of a federally documented vessel: The captain can order whatever meds he needs, including narcotics, for the vessel. Usually from a dispensary pharmacy. And those aren't easy to find, but your local pharmacist should be able to puzzle it out and locate one.
Scrip from your doc? Technically, legal only for you. Scrip for the vessel? Legal for everyone aboard.