If you are not a frequent traveller then your credit card anti fraud detection may flag your foreign purchases as "suspicious" causing your card to be locked out. This happened to me a few years ago and it is very unpleasant to be stuck in a foreign country and unable to use your card. It takes a phone call to sort out which can be a major hassle when you are far from home trying to look up phone numbers and deal with roaming.
Solution: ring your card provider in advance and ask them to make a note about your trip on your account.