That way your bank will do the monetary exchange calculation, giving you the best possible outcome. You will get a much better rate than exchanging your $US for the local currency, then doing the transaction.

If you do like a little "walking around money," then look at the symbols on the back of your debit or credit card, and find an ATM that's on the same network. You can withdraw the local currency there. You may want to notify your bank before you go to avoid having them freeze your credit or debit card due to an overseas transaction.

Recently heard Clark Howard discuss using your cell phone overseas (link):

"The first two exceptions to the overseas ripoff rule are T-Mobile and Sprint. Both include with their plans the use of their phones outside the U.S. That means in most countries you pay nothing for texting, nothing for unlimited data and about only 20 cents per calling minute.

The third exception you need to know about is Project Fi. If you travel overseas frequently, you should become familiar with this little known cell phone service from Google.

If you don’t want to leave AT&T or Verizon, the best thing you can do is buy a local SIM card for local service when you get where you’re going. For about $15 or $20, you can usually find one that will give you more than enough data for a month."