These drones would need to be armed since they'll be carrying cash and will be juicy targets.
Drone should only be sent out empty on a pickup and return to base full flight. There's a number of YouTube videos of quadcopters flying in the middle of fireworks going off. I think they'll be safe at that cruising altitude, and doing VTOL.
Where it gets tricky would be instant payment/instant delivery, if someone wanted a drone to come to them, relay the video of the QR code and the money being deposited in the payload container (without a counterfeit check) to the pilot/seller, and wait for a confirm.
If I were the pilot/seller, I would have the buyer fill out a form with their
BTC address and fiat amount they plan to deposit in advance, and send the drone under
these conditions. Once the drone returns back to base, the money would be counterfeit checked, and the
BTC sent.