If it was a one time thing, some tape and string, I’d just hover it and they’d snip it.
If this was something I wanted to do frequently, there are fairly cheap attachments that you can drop things with, which would be more fun, and I wouldn’t have to worry about the person snipping the string tugging it and causing danger to themselves and/or the drone.
They’re a battery, little servo to move a pin, and usually a photosensitive trigger, and you can drop things by turning the auxiliary/landing light on or off.
Here’s the first Amazon result for that type of device it’s $37 and has a max payload of 500 grams.
https://en.m.wikipedia.org/wiki/Decimal_separator