In case some of you don't know what the Fourbie is, it's the red truck that you use to go places. There is a trick to get opals while riding the Fourbie. It only works once per game. Not game as in the entire disc, but game as in a single file. The trick is to hold down the R2 button while driving on the road in the Fourbie and hold the the left analogue stick to the left or right. It doesn't matter which way you hold it though, as long as it makes the Fourbie turn in circles. After a few seconds of spinning, you'll get some opals. You can use opals to buy stuff. Enjoy this nifty little trick!