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.

Easy achievements - Accomplish the indicated achievement to get the corresponding number of Gamerscore points:

High Roller (20 points): Complete all story missions in Las Paradiso.
Destroy All Humans! (20 points): Destroy 1,979 Humans.
A-Lister (20 points): Complete all story missions in Sunnywood.
Zen Master (25 points): Complete all story missions in Shen Long.
Big Fromage (30 points): Complete all story missions in Belleville.
Furon Commander (35 points): Complete all story missions on the 4th Ring of Furon.
Pox's Apprentice (20 points): Complete half of the Odd Jobs in the game.
The Emperor's Agent (40 points): Complete all odd jobs in the game.
Sacred Son of Arkvoodle (30 points): Activate all of the landing zones in every invasion site.
Apocalypse Right Now (90 points): Complete all Missions, Odd Jobs, Challenges, and unlock all Landing Zones.
Biologist (20 points): Collect 10000 Furon DNA.
Biochemist (25 points): Collect 1000000 Furon DNA.
Brain Surgeon (30 points): Collect 5000000 Furon DNA.
Sleeps with the Fishes (20 points): Destroy 15 Mobsters in Las Paradiso.
THQ 1138 (20 points): Destroy 15 Lunarian Thugs in Sunnywood.
Fist of Furon (20 points): Destroy 15 Triads in Shen Long.
The Francodyne Connection (25 points): Destroy 15 Francodyne Guards.
Red Scare (35 points): Destroy 25 Red Nexosporidium Warriors on the 4th Ring of Furon.
Massive Damage (20 points): Trash 500 vehicles.
Paradiso Pursuer (20 points): Find all the Furon Crash Test Dummies in Las Paradiso.
Sunnywood Seeker (20 points): Find all the Furon Emperor Statues in Sunnywood.
Shen Long Scout (20 points): Find all of Pox's Record Collection in Shen Long.
Belleville Beneficiary (20 points): Find all the Furon Nails in Belleville.
Furon Factfinder (20 points): Find all the Lava Lamps on the 4th Ring of Furon.
Fist Master (20 points): Use the Temporal Fist 75 times.
Carnie (20 points): Beat the Furon Librarian's high score in all of the Humania Games.
Shock Trooper (20 points): Shock 100 humans with the Zap-O-Matic.
Proctologist (20 points): Probe 100 humans with the Anal Probe.
Horticulturist (20 points): Feed 100 humans to the Venus Human Trap.
Furoball Dribbler (20 points): Bounce 100 humans with the Superballer.
Furon in the Sky (20 points): Liquify 100 buildings with the Death Ray.
Flyswatter (20 points): Take down 100 airborne enemies with the Seeker Drones.
DAHM Master (25 points): Find all 8 DAHMs.
Pro-Pain (10 points): Las Paradiso - Shoot a Propane tank cluster to blow up a building.
The 'Wood (10 points): Sunnywood - Destroy "SUNNY" on the Sunnywood sign.
Globeclotter (10 points): Sunnywood - Destroy several humans within 3 seconds with the globe.
Donut Holed (10 points): Sunnywood - Throw a civilian through the donut hole.
Definitely Not in Kansas (10 points): Shen Long - Unleash the Tornadotron to throw tons of shipyard crates in the air.
Monkish Bowling (10 points): Shen Long - Use the bowling ball to bowl over at least 3 monks with a single throw.
Barge Boomer (10 points): Belleville - Destroy the barges.
Arc de Umph (10 points): Belleville - Throw a human above the Arc.
Crypto Sutra (90 points): Complete all Paths of Enlightenment.