Lori, we just returned yesterday from cruising on the Norwegian SKY.
One of the more interesting "hidden costs" of our cruise was tipping on bar bills. We aren't big drinkers, but enjoy sodas or fruit smoothies. The 15% gratuity from these items isn't very large, so everytime we wanted a soda, juice or whatever, we'd end up adding to the tip.
It really added up over ten days. Also, the available "free" beverages on the ship were coffee, tea, milk and water. The "free" water was heavily chlorinated. There was juice at breakfast, but the rest of the time, juice was $2.00.