This morning I called my credit card companies (I carry both a VISA and a Master Card, because often only one or the other is accepted) to let them know I would be traveling internationally. This puts and alert on my account as there where I will be and for how long.
Credit cards are, by far, the easiest form of payment while traveling. But they can also be a right pain in the bottom! I can't count the hours I have spent on the phone with credit companies working out the details of using a card across boarders. When the amount is larger, or from somewhere they weren't sure you should be (even though you told them you were traveling around Western Europe) they will put a stop on your credit card and it can take a magic rain dance performed upside down while singing a song you can't remember backwards to get them to reactivate the account.
However, more important than getting credit card companies to agree you are who you say you are calling from where you say you're calling from, is knowing what to do when things go wrong.
Some of the untold joys of traveling are pick pockets, theft, muggings, lost luggage or passports, and any number of illnesses. A lot of the more serious crime can be avoided with a little common sense. So before I go anywhere, I always have photo copies of all important documents (passport, credit cards, tickets, etc.) left with someone back home. This means that if the worst happens, I have access to important information to get the process started to get things back in order again. I also always have comprehensive travel insurance to rely on in case I get sick or my luggage goes on its own vacation without me. No one likes to think that things can go wrong, particularly while away from home, but it does happen. Putting a few safety nets in place is always a good idea.