I wouldn't put anything I value into either.
Likewise some may put virus into the disk (internally or automatically due to the virus itself) which the next person may not have their computers patched and have no anti-virus installed.
If I'd discovered one of these near my house in my early teens it would've obsessed me for weeks. I'd probably have ended up learning USB debugging or something to cause further trouble ;) I see this as an absolutely massive jolt to people's natural sense of curiosity which is so often neglected in urban environments.
And as for the potential for malware outbreaks, this is basically like a public water tap and just like we filter that water before drinking, scanning the data before using it will solve the malware problem.
If I were to use data from these drops I'd want a junk system that I could flatten between uses dedicated to the task. Connecting random usb devices to your system is a recipe for disaster in a billion ways. Even connecting well behaved usb devices to your system with unknown data on them is fairly risky due to the poorly chosen default settings of popular operating systems like Windows.
