Catch a Zigazoon as early as possible. Where ever you go and whatever you do, always keep the Zigazoon/Linoone in your party. Its Pickup ability will net you rare items throughout the game. Be sure to not to give him an item so he can pick things up. You can get anything ranging from Super Potions and Full Heals to Rare Candies, Full Restores, and even rare items such as King's Rock.