Go island hopping on the west coast
The west coast has the biggest variety of islands, making it the best place to go island hopping. Koh Phi Phi is the most famous island, but there are many others. Koh Lanta is a big and pleasantly developed island just next door, with mid-range resorts along Khlong Khong beach and a fun backpacker enclave along Long Beach. For more of a Robinson Crusoe feeling you’ve got islands like Ko Hai, Ko Yao Yai or Ko Raya. You’ll likely need to pay at least 800 to 1000 Baht a night for a bungalow on any of these islands (worth it, but good to know for shoestring travellers). For more island tips, consult some of the external links at the bottom of this post.
Get scuba certified (at ocean-bottom prices)
Thailand is the perfect country to learn how to SCUBA dive. Koh Tao is the most popular place to do so, with many dozens of internationally accredited dive schools. It takes just 3 days of training to become a certified Open Water diver. Read This: 6 Tips For Learning To Scuba Dive On Koh Tao