When the traveller goes from the US to Europe, he can get many unexpected expenses. It is so because the travellers usually use the credit cards to make the payments. That is correct. The cash can be stolen.
Though, if a person pays by credit card outside the US he has to choose the best plastics to pay with. Otherwise, he will get be charged foreign transaction fees or lose on money conversion.
The very basic rule to remember when a person goes abroad is that he should pay in local currency always. Whatever plastic the person has, he will be given options to pay in local currency. If the country the person goes to does not use dollars, the traveller should choose local currency option.