There is plenty to do wants you are there:

Jet Skiing
Paragliding
Horse Riding
Go Shopping
Speed Boating
Relax by the Hotel Pool
Take in a Lady Boy Show
Hit the sea for some Kyaking
Go Scuba Diving, Snorkelling
Hire you a moped or super bike
Farewell Dinner at Patong Beach
Try your hand at Deep Sea Fishing
A night out at the local clubs and bars
Have a Seafood Barbecue on the beach
Train at the all new Kata Muay Thai Gym

Visit Phucket Fantasy, where you can experience Thailands version of Disney World. Phucket Fantasy

But remember once there, chill, and relax man!! See here for Phucket