Traveling outside of the USA means that you will need to use local currency in many cases. Here are some tips:
1) a credit card is the best way to make purchases abroad. Please advise each credit card company that you will be traveling, and to which countries (this is not necessary with Amex). Also, confirm that the card does NOT have foreign exchange fees. Do NOT use a debit card for purchases. Don't rely solely on this method as sometimes credit cards may not be accepted or your charge may be blocked by your card issuer.
2) a good way to obtain currency abroad is to use your ATM card (for ATM withdrawals only, NOT as a debit card). Again, please advise your bank that you will be traveling and then ask about fees. Don't rely solely on this method as sometimes an ATM may not be available or work with your card.
3) About 3 weeks prior to departure is a good time to advise your local bank that you would like to obtain currency in advance of the trip, as they will likely have to order the currency. Ask your bank about service fees and if you place all of the currency orders together if there is only 1 service fee. The amount you bring is up to you, but keep in mind you should only need it for a tip on shore or purchases where a credit card is not accepted. You can also replenish by bringing US Dollars with you for later exchange. Usually these can be exchanged at local banks as needed.
If on a cruise or river cruise, sometimes the guest services desk can assist...but not always. I recommend about $25 to $100 US dollars worth of each local currency for each day you will be in an area requiring that local currency.