Can you buy a prescription in another country with a valid U.S. prescription?

First off, before everyone assumes I am some kind of junkie or fiend, this is a legitimate question, perfectly legal in any way shape and form, and please do not leave snide comments or rude remarks. My family is planning a cruise soon to celebrate a monumental occasion for my husband and myself. We would like to go on a cruise and have decided to go to either the Caribbean, the Bahamas, Mexico, or perhaps somewhere in South America. My husband has a medical condition and is prescribed several medications that he must take on a daily basis just to be able to move around and function. Some of his medications are considered a controlled substance. We are probably going to go on a lengthy cruise, maybe even one of those 2-3 week cruises. He is concerned that if anything were to happen (if we were victims of foul play or if some kind of accident occurred) that he would be stuck in another country or in the middle of the Atlantic without his medication and would be in severe pain. If he were to go too long without some of his medications it could very possibly be life threatening (and no I am not referring only to the controlled ones). What could we do to be prepared in an emergency such as this? Would traveler's medical insurance cover something like this? Assuming he had a copy of his prescriptions and a note from his doctor certifying what medications he is taking, would it be very difficult to fill them in another country? Would he be able to bring any medications on board that he purchased in another country if he presented his U.S. prescription? If he presented his U.S. prescriptions to a foreign doctor and that doctor wrote him a prescription, would he be able to bring it back into the U.S. without much hassle? We are not drug seekers or dealers or abusers. We are simply making sure we are prepared for any possible scenario! That way we won't have to panic if something were to occur, could handle it quickly and smoothly, and go about enjoying ourselves on our dream vacation! Any advice about traveling overseas with someone with a medical condition would be greatly appreciated. Thanks so much!