This is really the Big Kahuna of activities on the island. It operates fishing trips and rents gear. If you have a vague notion of something you'd like to do, come here and see what staff advise. It has a range of beach accessories such as chairs ($5) and umbrellas ($4).
Part gas station, part shop (which is crammed with sporting gear and idiosyncratic souvenirs), gear for rent includes mask and fins ($10/35 per day/week) and runs snorkeling trips (from $80).