This is an endgame mod. Or at least Las Venturas must be open.
You start with meeting Bosco near CJ's house in Groove street. He'll tell you what to do.

He'll ask you to find a random vehicle and bring it to a random location.
The code picks one of 141 vehicle models, including bikes, police cars, hot dog vans etc. I think I removed all mission vehicles from the list.
There are 22 locations, all SA covered.
When you arrive to this location - you'll find one of Bosco's men there. Just drive into the sphere and get your cash. Try not to kill the guy. In that case this job will be finished and you'll have to find Bosco in one of 22 locations and get another order. Radar blip is present both for Bosco and the delivery point.
So, deliver the vehicle and the guy will pay you and tell where Bosco is. Go meet him and get next order. Also, if you approach the guy on foot and enter the sphere (it will be small one) he'll offer you to end the current job (in case you're unable to find the required vehicle). If you agree - he'll tell you where Bosco is waiting for you.

When you enter a vehicle a news helicopter might start following you, you'll have to either hide or outrun it. There's a chance that an undercover cop will be after you (weak part of the script, he's too unskilled and easy to lose). After delivering the vehicle a rival gang of car thiefs might appear. Pay them, kill them or run away.

Next thing. When you're looking for the car you can press Insert key and a polaroid-style photo of the vehicle will appear on the screen. With text that will tell the model name and destination. Pressing Insert while looking for Bosco will also show text with his location. Vehicle photos taken from SA-MP wiki. A giant thanks to them.

Additional notes.
The mod saves it state in ini file. So, if you have an order from Bosco and Alt+F4 from the game - on the next load you will still have this order.

So, that's all. Nothing too complex. Just something to do while aimlessly driving around.