Supply Materials are packages dropped by Bearers when killed, or discovered in flotsam crates found floating in water. When opened, the packages contain random loot.
Flotsam has a chance (10% in the Exiled Lands, varies between 10-50% depending on location on the Isle of Siptah) to spawn at server start and a random respawn timer of 4-12 hours. A flotsam crate at a specific location will always provide the same variant of Supply Materials.
The loot is randomly selected from one of four possible loot tables. The same loot table can be chosen multiple times, allowing one to get much larger quantities of a specific type of loot if the same item from the same table is chosen more than once. The lower an item is in the list on its loot table, the less likely it is to be chosen from that table.
Items acquired from bearers will come in quantities equal to half of a full stack, while items acquired from flotsam will be one-tenth. All weapons given will always be completely broken.
Note: Currently, the fourth loot table for Supply Materials acquired from flotsam is bugged and will never be chosen.