I always keep the most recent prescription bottle when emptied, just in case I need to take a trip. As my insurance requires a 90-day supply on all refills, I don't need to take a full bottle with me on a 2 week trip. I will fill my older bottle with the amount necessary for the trip plus 2 days in case of any delays, or dropping of a pill to the floor which makes it unsanitary to take.

I always pack these original bottles in my carry-on or back pack, and have only been asked once at customs about the pills. As the prescription bottle with the original labels provides a description of the pill including markings, the officer was able to look at the pills and determine that they were the same as prescribed, and not something else in the bottle than what was prescribed.