For an easy first island outing without a long transfer, look at Khai I Love You Half Day (PNT). The short trip to Khai Island fits well into a schedule that avoids burning too much energy before the December 31 countdown.
For a first intro dive, compare Racha Island Daily Tour. It runs as a Korean-only program, so you can enjoy snorkeling and diving at Racha Island and Banana Beach without a language barrier, and included underwater photography makes it easy to bring back photos from the trip.
If you want a quiet daytime contrast to the busy countdown night, John Gray Seacanoe fits well. It is a full-day trip paddling through limestone caves and mangroves at a slow pace, so plan your return time carefully to avoid overlapping with the evening countdown.
To make the signature islands the highlight of your New Year trip, compare Phi Phi-Khai-Pileh-Maya by Speed boat (SeaStar) and 1 Day Trip Phi Phi - Bamboo Island Tour by speed boat (Seastar). Both are full-day trips around the Phi Phi area, but the first adds Khai, Pileh and Maya Bay while the second adds Bamboo Island. Choose based on how many days of your trip you want to spend island-hopping.
If you would rather stay active without a full-day boat trip, or worry about seasickness, look at Hanuman World & Luge and NOAH Catamaran Yacht Tour together. Hanuman World is a land-based activity with a zipline and luge that saves energy for the evening countdown, while the NOAH catamaran rides more steadily than a typical speedboat for a more comfortable day on the water.
If you have time left after checking out on the final day, [Last-Day Tour] Phuket Private City Tour & Airport Drop-off ties the routing together. It is a private tour that covers the city after you check your bags and continues straight to the airport, a clean way to close out a three-night trip.
Before booking, confirm pickup areas and times, maximum group size, whether meals or gear are included, and the free-cancellation deadline. Dry-season seas mean fewer weather cancellations, but the New Year holiday is peak season, and seats near the countdown and popular time slots tend to sell out first, so book as soon as your dates are set.