If you want to go off and explore the island by yourself, or just want the convienience of being able to get around then why not rent yourself a motorbike or mountain bike.
Be advised that many of the motorbike rental companies on the island are more interested in making money out of scratches and bike accidents than the rental incomes, so be careful if you do rent a bike. Ensure that you read the rental contract and ask to see the list of repair costs before renting as some of these can be extremely high, up to 5 or 10 times the cost of the replacement parts, we advise not to rent from the bike shops around the petrol station in Sairee as these bike shops in particular seem to be extremely keen on this scam. There are a couple of reliable rental companies in Mae Haad that we do recommend both Ollie's Bike Rentals and Island Travel Bikes.
Many of the roads on Koh Tao are not very good and so if you think that you may have problems with some of the roads to the more remote beaches it's best to park up your bike and walk down to the beach.
Another tip when renting a bike to look for a place where the bikes don't appear to be brand new, as this is usually a sign that the bike shop replaces any parts that get scratched immediately to make it easier for them to charge of any new minor scratches.