CheatOgre.com: Super Mario Sunshine

Return To The Airport
Once you've beaten the game (and saved your game), you will be able to go back to the Airport from the very beginning. It'll cost you, though. For the price of 10 coins, a boat close to the clocktower where you find Yoshi will take you to the Airport level -- which is filled with coins and fun stuff to do. Give it a try!

Sunglasses And Hawaiian Shirt
Want to see Mario in a different outfit than his trademark blue overalls and red shirt? How about putting on some shades and slipping into a shirt that would make even Tom Selleck jealous? The shades are easy to get. Look for a man with black sunglasses in the hub world (he's at the beach, close to the fruit stands) or in most of the other levels and talk to him. When certain conditions are met, he'll give you a pair of sunglasses to wear, which will darken your screen appropriately. 
Note: The sunglasses will disappear the moment you step into another level or restart the game.
 
The same guy will also give you a Hawaiian shirt, but you've got to do some work first: finish the game. If you've saved your game after you beat the last big boss, you'll be able to get your shirt anytime you talk to this guy.