Go to options screen , scroll down to cheat codes and enter YOUGOTIT to unlock everything.
Enter the following at the cheat code input screen.
|Enter MANYZEROS as a code.||1 million store points|
|Enter LITTLEGUY as a code||50cc bike class|
|Enter ONRAILS as a code.||All Bikes|
|Enter MORESTUFF as a code.||All challenges|
|Enter WELLDRESSED as a code.||All gear|
|Enter MCREWHEELS as a code.||All machines|
|Enter WHOSTHAT as a code.||All Riders|
|Enter FREETICKET as a code.||Freestyle tracks|
|Enter PWNAGE as a code||Paralyzer Monster Truck|