Go to the Press Start screen then go to the "New Game" screen. Now press Up, Down, Up, Down, Left, Right, Right, Y, X, X
Unlimited Ammo:
Go to the Press Start screen then go to the "New Game" screen. Now press and HOLD L + R and press B, Y, Up, Up, Up, Right
Get Time to Pay Mode:
Go to the Press Start screen then go to the "New Game" screen. Now press and HOLD L + R and press Right, X, X, X, B
Easy Mode:
Go to the Press Start screen then go to the "New Game" screen. Now press and HOLD L + R and press B, Left, Down, Down, Up
Unlock Unlimited Shotgun Mode:
Go to the Press Start screen then go to the "New Game" screen. Now press and HOLD L + R and press Y, X, Up, Up, Up
Unlock All Guns
Go to the Press Start screen then go to the "New Game" screen. Now press and HOLD L + R and press Up,Down,Left,Left,A,B,A,A