In California Games, one of the events you have to do is the BMX races. You do tricks for points, and the person with the most points wins.
And here's a way you can ensure that you will be the winner of the BMX event. First, make your way to the BMX event itself.
Then, hold down Select and press A to start it. Keep holding Select (the brakes) and then start pressing B repeatedly. Each time you do, you do a meager hop and get points.
You can do this as many times as you want for as long as you want, getting all the points you want.
And a turbo controller really helps pull this off.