how? it has to be a very very advance UAV that is not technologically feasible today... airdropping cargo like the Berlin airlift etc requires more than just piloting the aircraft. You need the loadmaster, the other folks that needs to unsecure the ropes prep the containers etc, open the ramp door and make sure it falls properly and all that. What if something gets caught or something goes wrong? How would you mitigate that if no one is on board?
It would not be possible to do it w/o humans inside doing the offloading and airdropping.