When you go through the Mimiga village collect the Map item and then use it to find a secret passage in the back room after defeating Curly in the Sand Zone. Use the Map to reach the end of the passage and use the 'Look' command on the ledge on the left to get Curly's underwear.
Do not trade in your Polar Star for the Machinegun. You will need the Polar Star and another weapon later in the game to trade for the Spur the most powerful weapon in the game. This weapon is also refered to as the charge shot as there is no need to collect weapon energy to power it up as all you need to do is hold down the firing button to charge your blast.
When you have made the rocket that leads you to the last cave, do NOT talk to Momorin to get the booster back. Instead use the rocket and keep your Mimiga Mask and there will be dialog changes after this point and some of the portraits displayed during the credits will be altered.