I’ve written before how you need to call your credit card companies and bank to let them know you’ll be traveling. This is true for a trip across the US or one to Europe.
What happens if a charge is something your credit card company doesn’t recognize? Do they call you? If so, do they have the right number to call? Does your phone work in Europe? Or, do they send a text which you won’t receive until you’re home?
Make sure you not only notify them, but that you leave the best contact information with them.