Enter these cheats during game play using controller in second port:

Hold L1 and press UP, UP, UP, UP - Have All Weapons
HoldL1 and press R2, R2, R2 - Full Health
Hold L1 and press UP, UP - Refill Ammo to Max Capacity
Hold L1 and press UP, DOWN, UP, DOWN - Infinite Ammo Toggle
Hold L1 and press TRIANGLE, SQUARE, CIRCLE, X - Massive Money Gain
L1, L1, R1, L1, L1, L1, R1, R1 - All Clothes
Hold L1 and press UP, LEFT, DOWN, RIGHT, TRIANGLE, SQUARE, X, CIRCLE - All Hobo fighting moves
Hold L1 and press UP, LEFT, DOWN, DOWN, TRIANGLE, SQUARE, X, X - All gym grapple moves

Unlockable costumes

Once you complete the requirements for the clothing, they’re automatically thrown in your closet, in all your safehouses.

Final Cut (New Coventry) houses all of the punk-esque items in the game. Worn In (Bullworth Town) houses more beachy, sporty, and middle classy type clothing. Aquaberry in Bullworth Vale houses all the upper crust type clothing, although until Chapter 3 the only clothes you can get in there are the Aquaberry Sweater and Vest.

Black Ninja Outfit - Fill up your yearbook completely.

Black Skate Shoes - Travel at least 50.00km on foot.

BMX Champion - Complete one of the bike races.

Boxing Outfit - Beat either ‘Boxing Challenge’ or ‘Prep Challenge’ in Chapter 2.

Crash Helmet - Place 1st in the Kart Race at the Carnival

Dunce Hat - Go to the boys locker room in the gym and turn on all the showers.

Edna Mask - Destroy 19/19 Tombstones during Halloween.

Fast Food - Complete the Burger Joint errand found in Bullworth Vale.

Firefighter’s Helmet - Pull the Fire Alarm 20 times.

Gnome Costume - Smash all garden gnomes.

Gold Suit - Buy all clothing in the game.

Green Ninja Outfit - Hit stuff with projectiles (eggs, etc.) 1000 times.

Grotto Master - Collect all G&G cards.

Jimmy’s Skeleton Halloween costume - Beating the mission ‘The Candidate’ will open up the mission ‘Halloween’ which unlocks the costume.

Orderly Uniform - Complete ‘Finding Johnny Vincent’ in Chapter 5.

Pirate Hat - Beat up pirate on island near Beach House.

Prison Uniform - Beat all the detention mini games at least once.

Red Ninja Outfit - During Halloween (must be done during Halloween) at Bullworth Academy, complete the Big Prank task.

School Mascot - Beat ‘Nice Outfit’ in Chapter 4.

Tiny Swimsuit - At the Beach House location, find the Preppie with a blue mission on the beach and beat his swimming time.

Wrestling Uniform - Beat Gym 1.

Originally from ToTheGame