Learn about local laws and regulations, preferably before you arrive on site, and obey them. Deal only with authorized outlets when exchanging money or buying items such as airline tickets and travelers checks. Adhere strictly to the local laws because the penalties you risk are severe. About 3000 Americans are arrested overseas each year. Despite repeated warnings, drug arrests and convictions are still a common occurrence.
Many countries have stiff penalties for drug violations and strictly enforce drug laws.
In other words, it is not worth imprisonment or extradition to break local laws.