Bring Euros! Lots of places don’t accept credit cards and if you have a card that charges you with foreign transaction fees, you’re in for a world of hurt. Double check with your hotel or cruise ship where are appropriate ATMs to get more cash if needed. Not all ATMs are created equal there! Also, a lot of countries have foreign currency exchange shops in frequent and convenient areas.
Side note: Croatia uses the Kuna, not the Euro. Some people accept the Euro, but most don’t. Here there are currency exchanges everywhere you look, so not a big deal to swap your Kuna for Euro and visa versa.
Tipping is acceptable at 10-15%, depending on the service.
If you go in summer, drink lots of water. It is HOT.
Try to learn some basic phrases in the language of the country you are going. Most people speak English, so no worries on a language barrier, but it’s a sign of respect.