In the title screen, hold down L1 + R1 and press any of the following sequences. If input a sequence correctly, you'll hear a good chime. Otherwise you'll hear a buzz. The cheats will only work in Single Player mode.

NOTE: For Xbox and GameCube, the buttons change from:
X to A / Square to X / O to B / Triangle to Y / L1 to L / R1 to R

Disable all HUDs: X, Square, Triangle, O
One-touch KOs in racing: X, O, O, X
Chicken-headed people: X, O, O, Square
High speed: O, O, Triangle, Triangle
Japanese Crash: Square, O, Square, O
Block car: O, O, Triangle, Square
Enable removed character lines: X, X, X, Square

Hidden Camera Modes: X, Triangle, Triangle, Triangle. To make use of this cheat, use the following instructions:

Plug in a second controller to your console. You will be using it to control the new camera modes that the cheat gives you. This cheat works not only inside the park, but also during races. The following buttons are all correspondent to the second controller, unless stated otherwise:

Select- Toggle hidden camera modes on/off.
Left/Right on D-Pad- Switch between camera modes.

Free Camera Mode
Left Analog Stick Up/Down- Move camera back and forward. You can zoom in and out of the level endlessly.

Left Analog Stick Left/Right- Move camera sideways.

Right Analog Stick- Use it to point the camera (as you would with first person's view).

L1- Ascend
L2 Descend

Reverted Fish Eye Lens Mode
Left Analog Stick Up/Down- Zoom in/out on Crash.

Left Analog Stick Left/Right- Rotate the camera around Crash.

Right Analog Stick Up/Down- Add/decrease the reverted fish eye lens effect. Use with Left Analog Stick simultaneously for better results. This is used to create a speed sensation.

L1- Move the camera directly to the top of the level, pointing down.
R1- Move the camera directly to the bottom of the level, pointing up.

D-Pad Up/Down- Switch the camera between characters (races only).

A second mode that acts like this one is available during races, but it's the exact same thing.

Normal Camera Mode
It's the same as the 1P camera, but it won't change angles during cutscenes. It's the only mode controlled by player 1.

D-Pad Up/Down (player 2)- Switch the camera between characters (races only).

Secrets

Credits Commentary (NTSC-only): To hear Cortex and N. Gin do a commentary over the game's credits, press the X button whenever a name is highlighted.

Loading Noises: In the loading screen, press the X button for a burp and the Triangle button (Circle on PSP) for a fart. Move the left analog stick up to make it high-pitched and down to make it low-pitched.

Taunt: When racing, press the L3 button (left analog stick inwards) to taunt. Each character has his/her own taunting animation and there's also a different taunt for each power-up being held.

Baby Crash Skin: Get all of the Die-O-Ramas to unlock this skin.

Skip Mystery Island (by Joshua Bywaters): This is more of a glitch than a secret, but it's possible to go to Happily Ever Faster as soon as the game starts. If you go to the entrance of Happily Ever Faster, stand on one of the sides of the closed bridge. With enough luck, you'll be able to jump inside. Progress of the game from here will be normal, and you won't ever have to go through Mystery Island.

Party Below Astro Land (by Crashnconker): Using the hidden camera modes cheat, take a peek below the floor in Astro Land. You'll find the entire main cast floating down there for some reason, along with a green spiked ball and the rising platforms.

Willie's Hideout (by Nise Krashoo): After you complete the game, use the camera modes cheat and, go to Von Clutch's statue in Midway. Go deeper into the foot path and you should find Willie Wumpa Cheeks, floating.

Unlockables

Vehicles (PS2/XBox/GC)
(Character - Tier 1 - Tier 2 - Tier 3)
Crash- Trikee - Yellow Horde - Crikey
Cortex- Imperium - The Deadinator - Probulot 2000
Pasadena- Harm Aid - Bad Girl - Le Chaux
Crunch- The Guzzler - Overcompensator - Bone Machine
Coco- Nostalginator - Bandibuggy - Fairy Mobile
Nina- Organ Grinder - Angsterator - Slave Driver
N. Gin- Extreme Slurpus - Junkulon Prime - Doom Buggy
Von Clutch- Zwergauto - Der Pickle - Pressurizer

Skins
(Mystery Island- MY/Happily Ever Faster- HEF/Tyrannosaurus Wrecks- TW/Tomb Town- TT/Astro Land- AL)

Crash- Classic Crash (MY)/Nega Crash (MY)/Agent Crash (HEF)/Cave Crash (TW)
          Mad Crash (TT)/Crizzash Bandicizzle (AL)/Realistic Crash (AL)/Star Crash (AL)
          Baby Crash (Get all Die-O-Ramas)
Cortex- Neo Fu (MY)
Pasadena- Embiginator (TT)
Crunch- Mr. Crunch (TT)
Coco- Princess Coco (HEF)
Nina- Part Timer (TW)
N. Gin- Cyborg Idol (HEF)
Von Clutch- Captain No-Sense (AL)