Activate the following cheats by entering the corresponding codes at "Main Menu" > "Extras" > "Cheat Codes".

CHEAT FUNCTION - CHEAT CODE
All Boards - MYPRECIOUS
All Championship Locations - FREEVISIT
All Leaf Sliding Locations - GOINGDOWN
All Multiplayer Levels - MULTIPASS
Art Gallery - NICEPLACE
Astral Board - ASTRAL
Bonus Mission 'Legendary Wave' in 'Pen Gu North' - DONTFALL
Customizations for All Characters - TOPFASHION
Monsoon Board - MONSOON
Play as Arnold - TINYBUTSTRONG
Play as Elliot - SURPRISEGUEST
Play as Geek - SLOWANDSTEADY
Play as Tank Evans - IMTHEBEST
Play as Tatsuhi Kobayashi - KOBAYASHI
Play as Zeke Topanga - THELEGEND
Tiny Shockwave Board -  TINYSHOCKWAVE
Video & Spen Galleries - WATCHAMOVIE
Unknown Code - THEARTIST

Unlock the following characters by earning the corresponding amounts of stage points:

CHARACTER - HOW TO UNLOCK
Arnold - Get 30,000 pts in shiverpool 2.
Big Z - Get 100,000 pts in legendary wave.
Elliot - Get 40,000 pts in pen gu north 3.
Geek - Get 60,000 pts in pen gu south 4.
Tank - Get 40,000 pts in the boneyards.
Tatsuhi - Get 15,000 pts in pen gu south 2.

Unlock the following accessories by earning the corresponding amounts of stage points:

ACCESSORY - STAGE POINTS
Back accessories - Get 30,000 pts in shiverpool 1.
Wrist accessories - Get 40,000 pts in pen gu south 3.

ACHIEVEMENT - HOW TO UNLOCK
Quick Learner (10 points) - Complete all the lessons in the tutorial.
Beginner's Luck (10 points) - Get 1 Trophy in Shiverpool area.
Leaving Shiverpool (20 points) - Get 2 Trophies in Shiverpool area.
Welcome to Pen Gu South (10 points) - Get 1 Trophy in Pen-Gu South area.
Leaving Pen Gu South (20 points) - Get 4 Trophies in Pen-Gu South area.
Welcome to the Volcano (10 points) - Get 1 Trophy in Volcano area.
Leaving Volcano (20 points) - Get 2 Trophies in Volcano area.
Welcome to Pen Gu North (10 points) - Get 1 Trophy in Pen-Gu North area.
Leaving Pen Gu North (20 points) - Get 3 Trophies in Pen-Gu North area.
Fashion Freak (40 points) - Unlock every accessory.
Board Collector (40 points) - Unlock all the boards in the game.
Shiny Stuff 1 (10 points) - Collect 25 Surf Idols in surf and leaf slide levels.
Shiny Stuff 2 (20 points) - Collect 50 Surf Idols in surf and leaf slide levels.
Shiny Stuff 3 (50 points) - Collect 100 Surf Idols in surf and leaf slide levels.
Slide Survivor 1 (10 points) - Beat the hi-score and get the shell in leaf slide 1.
Slide Survivor 2 (10 points) - Beat the hi-score and get the shell in leaf slide 2.
Slide Survivor 3 (10 points) - Beat the hi-score and get the shell in leaf slide 3.
First steps (30 points) - Start surfing on the Pen Gu North Legendary wave!
Lucky one (10 points) - Get 4 Shells.
Shell Collector (20 points) - Get 8 Shells.
Shell Lover (30 points) - Get 12 Shells.
Shell Addict (40 points) - Get 16 Shells.
Too Many Shells (50 points) - Get 20 Shells.
Record Man! (100 points) - Get 27 Shells.
The Beach Kid (50 points) - Unlock Arnold by getting the second shell in Shiverpool 2.
Wild Encounter (100 points) - Unlock Elliot by getting the second shell in Volcano 2.
The Geek (50 points) - Unlock Geek by getting the second shell in Pen-Gu South 4.
Figure from the Past (100 points) - Unlock Z by getting the second shell in Pen-Gu North legendary.
King of Boneyards (100 points) - Get a Trophy in Boneyards.