Go to X:17342, Y:4196 coordinates to find an easy place to keep
respawning C4 and grenades. Grab the C4 and grenades on the lower deck
by the water. Then, use your grappling hook and parachute to go a little
ways away from the area. Go back to the area now, and the C4 and
grenades should have respawned. Repeat this as many times as desired.