Some cruise lines sell a "soda sticker" or a special mug (WDW does the mug thing) that allows you to have unlimited soft drinks. Does NCL offer something similar? I don't drink much alochol but do drink diet soft drinks and tea.
the last cruise that i took was with ncl 3 years ago. at that time the tea was free and they did have a special pop card that you could buy for unlimited pop. i don't remember how much the card was, but they do have something for pop.