After completing the mission, Customs Fast Track, in San Fierro, you will unlock the ability to do the Exports and Imports side activity. This entails finding specific vehicles to bring to a cargo ship at Easter Basin, San Fierro. You will need to either use a crane to lift the vehicle onto the ship, or you can simply try to drive it on yourself, if the vehicle is small enough. There will be a list on the docks, showing the vehicles that are wanted, with there being three lists in total. That means you have to deliver 30 vehicles in total, and this side activity is needed for 100%, so if you’re going for that, then this will come naturally.