Yoshi's Spritzer Squirt:
Press R, then press A.

Avoid Dying:
During game-play pause the game just before you are about to die and then select Exit Area and you will be teleported in front of the level you were at and not lose a life.

Sunglasses and Shirt Pianta Location:
The Pianta man that gives you the sunglasses is located in the following
places in each level:

Pinna Park - Near the start point.
Bianco Hilles - Near the start point.
Ricco Harbor - Near the start point.
Delfino Plaza - Fruits Street.
Gelato Beach - Beach house.
Pianta Village - In the village during the daytime only.
Sirena Beach and Noki Bay - Not found in this level.