think this will need to be highlighted. Spoilers for things before the Deku tree (Dungeon 3).
It's really dungeon 2 because there is no BOSS battle on the spotlight island
1) The guy in the eskimo suit has the sail it is 80 Rupie
2) Check out the wind shrine on Dragon Roost Island first to get first WW song so you can control the wind for the girl toss.
3) use the sling hook on targeted enemies multiple times from a destance and gain 3 guaranteed items.
4) Beetle sales not only the bait bag and bait but a Pair that if you set down near a sea gull allows you to take control of the seagull.. very cool.
5) Before heading to the Great Deku Tree after saving the dragon go back to the island where you got the sail an talk to Todd, the dancing rainbow 70's guy at the top of the hill. then play random songs in 3/4. after a second he will teach you a new song.