Hidden car 

Complete all ten missions to unlock the homer car. Choose homer's picture at the car select screen to use Homer's car.

Holidays...

Set the PS2 system to following days to have the following character under the "?" at the character selection screen

January 1 - New Year's Krusty

October 31 - Halloween Bart 

November 22 - Thanksgiving Marge

December 25 - Christmas Apu