At the 'Main' menu go to 'Options' and select 'Cheat Codes' and enter the following codes to activate the corresponding effect.

Unlock ALL Arcade Mode Events:
Enter the code SLVRKEY

Unlock ALL Story Mode Events:
Enter the code GOLDKEY

Unlock ALL of Lightning McQueen's Friends:
Enter the code EVRYBDY

Unlock ALL Paint Jobs for ALL Non-Lightning McQueen Characters:
Enter the code CARSHOW

Unlock ALL Lightning McQueen Custom Kit Parts:
Enter the code GR8MODS