Not included:
Tips: roughly $11 per person per day is suggested. Budget it. This is really the only "required" extra; though technically it is optional the crew in tipped positions are paid virtually nothing in salary and so are dependent on tips.
Everything else is optional, and you can have a great cruise without spending another dime beyond tips, but most people do spend significantly more.
Excursions: (guided outings at ports of call) Can get expensive. They run from $30 to $100+ per person. If you do an excursion at each port of call on a seven-day cruise you will have a major additional expense.
Food and Drinks: All alcoholic drinks, "special" drinks like smoothies and specialty coffees, and anything ordered from a bar or lounge are extra, and have gratuity automatically added. This can add up. There is a supplemental fee ($10) for dining at Palo, but oh it is worth it! Concessions at the movie theatre are extra. Otherwise all your food is included, and all "normal" nonalcoholic drinks at meals or from the deck 9 beverage station are included.
Photos from Shutters cost extra, even your boarding photo.
Scuba gear, tubes, boat rental, and bike rental on
Castaway Cay cost extra.
Spa treatments are of course extra. Use of the fitness center and locker rooms is free.
Shopping both onboard and in port is obviously not included.
What have I forgotten?