After the game loads at the title screen there's a green "stickers" button, tap that and on the Stickers screen tap the top right button labeled "Enter #Tag". You don't need to type the # symbol, just the letters.

Effect	Code
Unlocks Goldfish reward	cool
Unlocks Raccoon reward	spin
Unlocks Rainbow reward	snow
Unlocks Seagull Reward	rays
Unlocks bonus levels in Bouncy Beach	dive
Unlocks bonus levels in Bouncy Beach	nice
Unlocks bonus levels in Bouncy Beach	sand
Unlocks bonus levels in Bouncy Beach	surf
Unlocks bonus levels in the Dusty Desert	fast
Unlocks bonus levels in the Dusty Desert	grin
Unlocks bonus levels in the Dusty Desert	jump
Unlocks bonus levels in the Dusty Desert	peel
Unlocks bonus levels in the Frosty Forest	cold
Unlocks bonus levels in the Frosty Forest	good
Unlocks bonus levels in the Frosty Forest	sled
Unlocks bonus levels in the Frosty Forest	wish
Unlocks bonus levels in the Grove of Goodness	kids
Unlocks bonus levels in the Grove of Goodness	soar
Unlocks bonus levels in the Grove of Goodness	star
Unlocks bonus levels in the Grove of Goodness	team