Koh Phangan

Bus: Bangkok to Suratthani
Most travel agencies will be able to sell an all in one ticket from Bangkok to Koh Phangan which includes the bus and ferry ticket for about 650 Baht per person.
Buses depart from Bangkok at around 7 p.m., arrival early morning in Suratthani in time for the first ferry to the islands. Coming back, there are numerous ferries, but for the bus you will need to depart no later than 1 p.m.
Usually a shuttle bus will drop passengers off in Suratthani to wait until about 7 p.m. at which time the bus will depart to Bangkok.

Train: Bangkok to Suratthani
Second Class (Air -con or Fan) Sleeper trains are the best as you get a table and sofa that turns into fairly spacious beds, the lower bunk is bigger so best.
First Class with sink and double bunks in each room.
All trains for Phangan stop at Suratthani railway station which is few miles out of town, so if have to stay in Suratthani, it is cheapest to lodge near the station otherwise you must rent a Songtaew Taxi.

Air: Bangkok to Suratthani
Koh Samui Airport is the most convenient airport with Bangkok Airways, flying in over 40 times in a day from Bangkok, Krabi, Phuket, Singapore, Kuala Lumpur or Hong Kong. The last boat leaves for Koh Phangan from big Buddha pier at 6.30pm and flights arriving later than 5pm, you may have hire a private speedboat or stay in Koh Samui.
It is cheaper to fly from Bangkok to the government airport at Suratthani where a couple of budget airline. it takes a minimum 0f 5 hours to get to Koh Phangan from Suratthani airport at a cost of around 450 baht which include bus transfer and boat ticket.