The Loot Carriers are drones manufactured by the Ship It! mailing company. Their purpose is (presumably) to deliver items to people living around the island. They were available in Hot Spots which are named POIs with golden names on them. There would be at least 1 named POI being a Hot Spot, and a maximum of 3 named POIs being a Hot Spot.
Shooting down the Supply Drones will make them fall on the ground and spawn Rare or above weapons.