First, let's take a look at the West Island Coast. This area is located to the west of the main game world and can be accessed by sailing your boat to the nearby beach. Once on the beach, look for a gun case located near the entrance. Inside the gun case is a Grenade, so be sure to grab it on your way to the next point.
The next stop on our journey is the River Fork. This area is located to the south of the main game world and can be accessed by taking the left river along the right bank. When you arrive at the river fork, take a look around until you spot a gun case located adjacent to the river. Inside the gun case is a Grenade, so be sure to grab it before moving on.
Finally, our last Grenade point can be found on the East Island side. This area is located on the east coast of the main game world and can be accessed by navigating your boat to the nearby beach. Once there, look for a bunker located near the beach and enter it through the cave. However, be aware that you need a VIP Keycard to enter the underground complex. Inside the bunker, you'll find a suitcase at the bar which contains the final Grenade.