• For credit card purchases, use a card issued by a bank that adds little or no surcharge to foreign billings. Among those banks are Capital One, USAA, and quite a few smaller banks and credit unions, and AmEx isn't bad.
• For cash, use a low-fee ATM card. If you're heading for Australia, Britain, Canada, France, or Germany, you can use a debit card from Bank of America without any fees at ATMS owned by one large bank in each of those countries. You can use a Citi debit card at Citi-owned ATMs in lots of foreign countries, although Citi's coverage is spotty in many places. Debit cards from quite a few smaller banks also allow no-fee or, at worst one percent fee, withdrawals from foreign ATMs.
• Do not use a credit card for local-currency cash advances; do not use a debit (ATM) card to withdraw foreign currencies in small amounts.

Next week, I'll provide more extensive comparisons for some of the largest banks and credit-card issuers.