Visiting Croatia and Turkey on a Mediterranean Cruise?

My lucky son is earning a high school credit, studying and travelling on a cruise ship through the Mediterranean this summer. He phoned this morning and said he's learning a lot, having a terrific time, and that Istanbul is the most beautiful city he's ever seen. While worrying over how much spending money to send with him--and in what currency, my husband read a couple of blogs that said that while Turkey and Croatia use their own national currencies, Euros are preferred. So we sent him with Euros, and some American dollars to use on board the ship. But my son just phoned to say the blogs weren't correct--with limited time and in a travel group, it wasn't easy to find places that accepted or exchanged Euros in Split, Dubrovnik and Istanbul. So if you're going on a Mediterranean cruise this summer and will visit these places, take small amounts of the national currencies with you, or make sure you have a bank card or credit card with you and know your PIN number so you can make a withdrawal at an ATM machine onshore.