Preparation
Documents: Do not forget passports, identity cards, and driver’s license (if you need to rent a car). You also must have a credit card (one for each stateroom is enough). Cruise will link your cost on board to this credit card. After the trip, you can leave the ship directly and wait for the bill at home, otherwise, you have to pay a lot of cash as deposit first and handle your account before you leave. Very troublesome!
Clothes: You can pack most comfortable and casual clothing for daytime. Most ship do not have very strict rule for clothing. I did not see anyone in a night gown. Just do not ware swimsuits and jeans, T-shirts in the main dining room. I saw people wear all kinds of clothes in outside eating area and relatively formal shirts in other restaurants.
Other things: For excursions, I need sun glasses, hat, sun blocker, sport shoes, beautiful skirts, cash, coins (for buying bus or train ticket), umbrella, map, lonely planet, and jacket. When traveling to tropical areas, it's a good idea to carry insect repellent. I always take my passport with me when I leave the ship.
I also packed essential medications with me, although you can find basic medicines from the ship, it will cost you a lot for seeing a doctor on board.
Always to take your own camera, it is very expensive to buy the photos from cruise photographer. If I remember correctly, one photo of myself would cost me 23USD in Norwegian Epic.
I brought my computer, but I did not use internet on board. As it would cost me 100USD for using it for 200 minutes. The speed is slow and Skype or other video call is not possible.
Norwegian Epic has European outlets in every cabin. I am sure about other ships, so a universal converter is handy. New ships usually provide hairdryer. If not, to sit on the deck for an hour, my hair will be dry.
I printed maps from google map for all the ports, train stations of each port city or city we planned to visit and places of interest. The maps were very helpful.
Transportation:
I spend 99Euro/per for return air ticket between Amsterdam and Barcelona. I choose KLM over budget airlines as I can check in up to 23kg of luggage.
I did not choose excursion trips offered by my cruise, as they are too expensive. An 8-hour trip easily costs more than 150USD, while I planned myself and only cost 30 Euros for the same amount of activities.
