It's generally approx. one and a half servings of any dish, so just look at the serving number and and multiply by 1.5 to see what you'll need for the cruise. One exception that I know of is hamburgers, which requires 2.5 servings. But generally, I try to overstock the **** out of what is being requested, so I don't follow this too closely. I just constantly cook the 20 dishes I'm stocking once I'm done with one day's task.
Hope that helps! Let me know if it wasn't clear.