My suggestion, drop hopperoutput and fuelStorage loot when entity death with option to choose the prefab that will be created: backpack, loot_drop..

	private void OnEntitySpawned(BaseNetworkable ent)
	{	
		if(ent is MiningQuarry)
		{
			var entity = ent as MiningQuarry;
			var hopper = (entity.hopperPrefab.instance as StorageContainer);
			var fuelStorage = (entity.fuelStoragePrefab.instance as StorageContainer);
			hopper.SetParent(entity);
			fuelStorage.SetParent(entity);
			// hopper.inventory.capacity = 36; // if want to change te capacity
		}
	}

	private void OnEntityKill(BaseNetworkable entity)  
	{
		if (entity is MiningQuarry)
		{            	
			StorageContainer[] containers = entity.GetComponentsInChildren<StorageContainer>();
			foreach (StorageContainer container in containers) {
				container.DropItems();  
			}
		}
	}

I did for me.