There should be a "fine print" on any cruise search that says something like "price includes cruise, port fees, but not government taxes, gratuities, excursions......." etc.
Included food is available for all meals. We rarely do a specialty restaurant or other pay-for items.
The biggest costs beyond the price of the cruise is probably gratuities, which can be paid for ahead of time, and excursions, if you choose to do any. Some people buy beverage packages. Many family-friendly beverages can be had free of charge (juice, coffee, tea, iced tea, etc.) On a big ship there will be some rides and activities for which there is a charge.