Codes
NR2A-EAD4 = Start with 99 shots
RHCA-E6Y2 + RHCA-E6Y4 = Infinite ammo when standing
RHYT-E61T + RHYT-E61W = Infinite lives
ADZT-EACC + RGZA-A6YJ + RGZA-6AYL = Infinite Health

Passwords
Garfield may have been caught, but you won't if you use these passwords.
Boss 1: Teacher, Garfield, Odie
Boss 2: John, Pooky, Arlene
Boss 3: Teacher, Pooky, Garfield
Boss 4: Odie, Odie, Arlene
Boss 5: Waitress, Pooky, Garfield