No, you do not have to book the tender. Normally first thing in the morning, it can be a little hectic, as a lot of people want to get off the ship at the same time. You just have to get in line and take your turn. They always have more than one tender to take. This happens the same way when you come back to the ship. (Just "remember"
where you got off the ship, so you can go back to the "same" place. Also make sure you note the TIME you have to be back on ship, as they will not wait for you to get back on the ship. Give yourself at least an hour to be back on the ship before it leaves port.) You will have to get in line again, to get your tender to take you back to the ship from the island that you are on.