Always be sure you have some foreign currency to cover most circumstances. Before you go, check the Internet to learn both the historical and current currency exchange rates for your destination on www.xe.com. XE also has a free app (over 20 million downloads!) that converts every world currency, including bitcoin. The app even stores the data, so it’ll work even when you don’t have internet access. See it here: http://www.xe.com/apps/
You can buy foreign currency from your bank, but the best exchange rate with the least amount of fees will probably be from the ATM at the airport when you arrive. There are currency exchange offices near the baggage claim in most international airports and they tend to be open when the international flights arrive. They are a safe but fairly expensive option. If you exchange large amounts, they may offer a discount buy-back program. Be sure to ask.
Some also offer the option to give you a debit card you pre-load with cash. This is an “all of the eggs in one basket” answer and not your best choice. On the other hand, you could use it to give some preset spending for kids, etc. Just remember, if the card gets lost or it’s stolen, everything is gone.
Also, always avoid offers to exchange currency on the street, particularly in tourist areas. The currency they offer you will likely be counterfeit or part of some black market scheme.
For more than 25 years, Steve was an intelligence community professional who traveled and lived throughout Europe, Asia, the Middle East, Sub-Saharan Africa, and Central America. He now uses his experiences and formal training to help people overcome their reluctance to travel by giving them the solid, reliable information they can use to plan effectively, reduce risk, react to danger, and return home safe.