Type in GOLDRUSH as a Profile Name.  This will give you All ATVs, Bonuses, Riders, and Tracks

Unlock All Riders

Type in BUBBA as a Profile Name.

Unlock All ATVs

Type in GENERALLEE as a Profile Name.

Unlock All Tracks

Type in ROADKILL as a Profile Name.

Unlock All Tricks

Type in FIDDLERSELBOW as a Profile Name.

Unlock Max Stats

Type in GINGHAM as a Profile Name.