Would using a drone to pay for something count as commercial use?
Laws around drone use are very new, and the only way to be certain about this is to have a case come to trial. You probably don't want to be the person it comes to trial over. A lawyer would give you a much better interpretation, but even they can't be sure.

If you are interested in my personal uninformed opinion (IANAL) then I think it would not count as commercial use. My reasons are:


The drone is completely incidental to the transaction. The cashier would do exactly the same if you showed up in person on foot or in a car, or if you sent someone else to make the transaction.
If you drive your car to McDonalds, that does not count as commercial use of your car. If you fly to McDonalds  then that does not count as commercial use of an aeroplane.