Regarding credit cards overseas--much/most of the world uses "chip and PIN" credit cards and any (remaining) US card that uses only a magnetic "swipe" strip is useless. Even if you have the now common credit cards with a "chip", you need to have an associated PIN to use these cards in much of the world (the US will adopt this too, eventually). So, contact your card issuer and get a PIN to go with your present card, and ask them to be sure it will work with the "chip and PIN" technology where you are going.
As Audrey mentioned, the foreign transaction fees differ between card issuers, so even if getting a new card isn't worth the trouble for a single trip, at least find out what your existing cards charge and use the one with the lowest fee. Visa and Mastercard are widely accepted, AMEX less so, and Discover is a rarity (nonexistent?) in the places I've traveled outside the US.