There is no need whatsoever to write down account numbers. Any CSR can locate the appropriate accounts by asking the appropriate personal questions (including the heralded SSN) when you call. More important: Add the overseas customer service numbers to your palm, blackberry, ipod etc. so that you have them handy if needed, and maybe send yourself an email (with scanned passports) so that you can access them from the internet in the event you lose everything.

Packing account #s and copies of cards in luggage is just like sending out an invitation to fraud. And don't forget to put your backup cards (and passports) in the hotel safe when not in use.