We haven't gone on our Baltic cruise yet, but from what I've read, the only country using the Euro is Finland. In Russia, most places seem to take either credt cards or dollars. We're using a private guide in St. Petersburg, and we've been advised that the guide will buy anything for which rubles are needed, and we can reimburse her in dollars. It has sounded like sometimes local currency is needed for local transportation in Stockholm and Copenhagen. Most people seem to get local currency at an ATM, which offers a better exchange rate.