Thailand has very few true all-inclusive resorts, and almost all of them are in Phuket and Khao Lak. Only two run all-inclusive as the way the resort works, Club Med Phuket on Kata Beach and Hotel Riu Palace Phuket on Mai Khao, whose plan runs 24 hours. Everywhere else, all-inclusive is a package or meal plan sold on top of a room rate, often through tour operators, so the same resort can be all-inclusive on one booking and breakfast-only on the next. This list ranks the 12 where you can really book it, resort-run plans first.
Outside Club Med and Riu, a Thai all-inclusive usually means three meals at one or two of the resort's restaurants and house-brand drinks, local beer, house wine, cocktails and soft drinks, served from about 11:00 to 22:00 or 23:00. Premium drinks, room service, the spa and excursions are almost always extra. Barceló Coconut Island's own terms are typical, with house drinks from 11:00 to 23:00 and half price after that.
Many resorts that other lists call all-inclusive publish no all-inclusive plan of their own, among them Centara Grand Phuket, Katathani, Kata Rocks, Phulay Bay and Dusit Thani Krabi, so they aren't on this list. Read the board on your rate before you pay, because that line decides what you get.