Remember, Credit cards used at foreign ports may have additional charges for exchange rates and service charges added to every transaction, always verify.
It is in your best interest to contact your credit card company before your departure and let them know the destinations you will be visiting and the dates, it is common for a block to be put on a credit card, if the credit card company determines your account may be compromised.
Always have the toll free numbers contained on the back of your credit card on your person, while in port, also having the port agent at each port of call is very important, in case of a delay back to the ship or other matters that may require assistance from a person with knowledge of the customs and laws.
The port agent is your direct link to the ship!
Cash is king, however you may end up paying higher prices for items purchased with US Dollars vs local currency.
One fact to remember, you don't need your passport while in port to get back on the ship, however if you miss the ship and you need to catch a international flight to the next port of call, you will not be able to purchase the airline ticket without your passport.
Did you know that if you experience a major medical episode or have an accident or in the opinion of the ships captain or doctor you may be a liability to the cruise line, you will be denied boarding.
You will need your credit card or you will need to arrange payment to a medical facility, if you require any medical treatment!
Most travel cancellation policies purchased before the cruise are secondary coverage and or medical plans here in the USA only reimburse for medical payments received, as long as it was pre-approved.
This is why ever (passenger), whom has any medical coverage should have the phone number for pre-approval for medical treatment and the form(s) most medical policies will require to be completed by treating physician.
Another tip, Have your e-mail on the front of your passport with the words "CASH REWARD UPON RETURN".
I hope this will shed some light and further assist on safer travel.