Mission Skip:
Quicky press R, L, R, L, R, L, X repeatedly. A message will confirm correct code entry.

Show Hidden Drug Stashes:
Quickly press R, L, R, L, R, L, Left. A message will confirm correct code entry.

The Refinery:
Repeatedly press L + R + B + A. A message will confirm correct code entry.

All Weapons:
Quickly press R, L, R, L, R, L, then click the Right Analog-stick. A message will confirm correct code entry.

Infinite Ammo:
Enter the inventory screen. Quickly press R, L, R, L, R, L, Down while on a weapon. Only the weapon that was highlighted will have unlimited ammunition, and the code must be repeated for each weapon. A message will confirm correct code entry.

Invisibility:
Quickly press R, L, R, L, R, L, A. A message will confirm correct code entry.

All Drugs and ,000:
Enter the inventory screen. Quickly press R, L, R, L, R, L, then click the Left Analog-stick while not on a weapon. A message will confirm correct code entry.

Unlock Bonus Mission:
Collect all 25 secret stashes in Asia.
Unlock Original 1988 Arcade NARC:
Collect all 25 secret stashes in USA