At the "Extras" menu, select the "Unlock Content" option. Enter one of the following codes to unlock the corresponding bonus. Then, select the "Customize" option at the "Options" menu to activate the unlocked bonus.

Saucer attachments - Enter "V81fvUW3" as a code to unlock the Saucer attachments.
Saucer skins - Enter "X91mw7zp" as a code to unlock the Saucer skins.
Biker costume - Enter "1gb57M2x" as a code to unlock the Biker costume.
Chef costume - Enter "51c24KiW" as a code to unlock the Chef costume.
Gangster costume - Enter "J5d99bPz" as a code to unlock the Gangster costume.
Kung Fu costume - Enter "Ly11r98H" as a code to unlock the Kung Fu costume.
Mime costume - Enter "7qd33J1n" as a code to unlock the Mime costume.
Velvet costume - Enter "F9sT5v88" as a code to unlock the Velvet costume.
Seventies costume - Enter "S63bf2kd" as a code to unlock the Seventies costume.
Sixties costume - Enter "M13Ni95L" as a code to unlock the Sixties costume.

Completion bonuses - Successfully complete the game to get approximately 3,000,000 DNA and have ammunition recharge for your non-selected weapons.

Destroy All Humans! reference - Go to the Space Dust in Las Paradiso. Look closely at the movie posters to find an ad for the original Destroy All Humans!

Mario, Sonic, and Halo series references - When you do the first story mission in Belleville, France, Pox will start talking 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" (a reference to the Mario series), "You're a really fast hedgehog" (a reference to the Sonic series), and "You're a space marine on a planet with a ring around it" (a reference to the Halo series). Pox will say all those ideas suck and then makes up his own idea.