Here are The Traveling Professor's tips for exchanging currency in Europe.
Get Cash from an ATM: This is by far, the easiest and cheapest way to go. It is important to give banks travel notifications before departing, otherwise cards may be rejected. Of course, get a card with no transaction fees or withdrawal fees.
Pay the Dinner Bill for the Group: On our small group tours, we may go out for dinner with 6 people for instance. If cash is needed, offer to pay the entire bill on your credit card and collect the cash from others.
For Small Amounts of Cash and Coin: Here's a tip probably not seen anywhere else: what if only a few euro or coins are needed and all you have in your wallet are US dollars? Certainly it is not worth it to take money out of an ATM and exchange bureaus charge killer fees. Believe it or not, those who take tips in coins (tip boxes in restaurants/cafes or lavatory attendants for example) are usually happy to accept your dollars and coins (or any currency for that matter) in exchange for their coins.
Don't Use Exchange Bureaus: The commissions are outrageous.
Don't Get Money from a Bank Before Departure: Expect to pay a 7%-12% commission if you do. Upon arrival, almost all airports have ATM's.
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