Snake River Canyon level:
Enter LASTSTAGE as a password

Grand Finale mode:
Enter LEVELS as a password.

Only have normal levels:
Enter RESET as a password.

Glitch: Invisible ramp:
After completing the five levels in the Las Vegas level, on the Grand Finale, choose stretch limos as the thing to jump. Set the number of them to the maximum and put your settings to the first three of them very good, and leave the bottom two alone. Take the jump and you will hit an invisible ramp above the real one, making it easy to land and get a lot of money.