Halloween mode:
Set the system date to October 31 to unlock Bart in a Frankenstein costume.

New Year's Day mode:
Set the system date to January 1 to unlock Krusty in a tuxedo.

Thanksgiving mode:
Set the system date to the third Thursday in November to unlock Marge in a pilgrim dress.

Christmas mode:
Set the system date to December 25 to unlock Apu in a Santa costume.

Car built for Homer:
Complete all ten levels in mission mode to unlock the car built for Homer.

Hint: Extra time:
To get +2 seconds, hit the phone booths that have Mr. Burns' picture on them.

You can get +2 seconds in the road rage levels by running over the Transit bus stops.

Hint: Mission skip:
Intentionally fail a mission five times and it can be skipped. Note: This cannot be done on the final mission.