Unlock the following items by entering the corresponding codes at "Extras" > "Unlock Content". Then, select "Customize" at the options menu to activate the unlocked items:
CHEAT FUNCTION - CHEAT CODE
60's skins (crypto) - M13Ni95L
70's skins (crypto) - S63bf2kd
Biker skins (crypto) - 1gb57M2x
Chef skins (crypto) - 51c24KiW
Gangster skins (crypto) - J5d99bPz
Kung fu skins (crypto) - Ly11r98H
Mime skins (crypto) - 7qd33J1n
Saucer attatchments - V81fvUW3
Saucer skins - X91mw7zp
Velvet skins (crypto) - F9sT5v88
Complete the game to get 3 million DNA and ammo recharge for your non-selected weapons.
Destroy all humans ad:
Go to the space dust in las paradiso. If you look closely at the movie posters there is an ad for the original destroy all humans.
Destroy All Humans! easter egg:
Go to the Space Dust in Las Paradiso and look carefully at the movie posters to find an ad for the original Destroy All Humans!.
Halo easter egg:
During the mission in the Las Paridiso military base, Crypto says "Maybe we should have brought the Master Chief along."
Mario, Sonic, and Halo series easter egg:
When you do the first story mission in Belleville, Pox will talk about video game ideas. Crypto will say "You're a plumber, but you don't use plumbing stuff to kill your enemies, you just jump on them", "You're a really fast hedgehog", and "You're a space marine on a planet with a ring around it". Pox will say that all of the ideas are crappy and then makes up his own idea.
Monty Python And The Holy Grail easter egg:
In Belleville, the S.W.A.T. and the army will say ridiculous insults, such as "I fart in your general direction!" and "I wave my private parts at you, you son of a silly person!" These are insults from the movie Monty Python And The Holy Grail, in which the protagonists are taunted by French guards with these exact quotes and many others.