How do you get to farmers island?

Go to the boat highlighted on your map. You can swim out it then select it with your action button. Don't start driving the boat! You'll waste gas and this is bad if you don't have enough for a round trip. Open your map and look around by dragging until you find Farmer's Island. Tap on it and you'll get a dialogue box that says you need x amount of gas to get there. Keep in mind you'll need the same amount to come back! You should be able to find some on the new island, though. It'll zip you almost right up to the island! You can taxi in the boat a bit or swim.