Enter the following codes during gameplay.

Key:

[L] = While holding L press...
[R] = While holding R press...

[/L] = Release L
[/R] = Release R

Invincibility:
[L] A [R] X, Y [/R] A [R] X, Y, B, A, Black, Y, Black [/L]

Infinite ammo:
[L] A [R] X, Y [/R] A [R] X, Y, B, A, Black [/R] B [R] Back button [/L]

Infinite lives:
[L] A [R] X, Y [/R] A [R] X, Y, B, A, Black [/R] A [R] Back button [/L]

Extras:
[L] A [R] X, Y [/R] A [R] X, Y, B, A, Black, B, Back [/L]

Special thanks to Revolution reader John Knight!