For a sound test, enter the password "JOURNEYS.END"
For access to six bonus levels, enter the password "BONUS.LEVELS".
The password "LOADSOFSTUFF:" grants unlimited ammo for any weapon you acquire. The colon at the end is not a typo.
For an indestructable car, enter the password "I.AM.IMORTAL".
To warp to the endgame, enter the password "ENDGAMELEVEL".
To select any level, enter the password "RABBITBADGER".
To gain all weapons at the start of the race, enter the password "ALL.TOOLEDUP".