FWIW, here is the sum total of guidance on throwing stuff out of your airplane in the US.
Sec. 91.15
Dropping objects.
No pilot in command of a civil aircraft may allow any object to be dropped from that aircraft in flight that creates a hazard to persons or property. However, this section does not prohibit the dropping of any object if reasonable precautions are taken to avoid injury or damage to persons or property.
I've participated in airdrops from both ends, it can come in handy at times.