These are the unlockables in the game, which have been verified against the official game website (for accuracy. Input the following codes on the main menu for higher game functions: Current weapon becomes bolt action rifle. Adds 999 rounds to current weapon magazine. Invulnerability (damage visual still present).
On the title menu with the words Play, Options, Extras, hold L + R (click) and input DOWN, X, UP, Y, DOWN, DOWN, UP, UP and release all keys to get the cheat menu.