Need to make some quick cash in Grand Theft Auto V? Use this in-game exploit to earn (possibly) infinite stacks of money right after touching down in Los Santos.
Scattered around the map are a dozen or so "Shipwreck Packages." They're located underwater off the coast, but are usually in locations that you can swim to. Once you find one, you can earn as much money as you want from it, providing you don't leave the area or switch characters for too long.
As long as you aren't being pursued by police (having a wanted level prohibits you from switching characters), swap from the character who picked up the case - i.e. Franklin to Michael or Michael to Trevor. Immediately switch back to your original character and you'll find that the package has reappeared, and your oxygen has been replenished. Repeat this as many times as you like to earn as much money as desired.