hey, so a bit late to the party but I've had similar thoughts before.
one idea I had was combining digital dead drops with geocaching.
like using it to hide encrypted messages that lead to "secret" caches or something for those who want to take things another step further.
one way to do this would be to setup something like a pi-zero-w so that a guest account is setup upon login, cleared after log off, and this gives access to the files without allowing upload of files to prevent obvious problems.
maybe the password could be gained via a gadget cache type thing, or even have the file accessed through a control interface or something with a small LCD screen.
there's tons of ideas there that could be interesting because who doesn't bring their phone everywhere these days and even the cheapest flip phones can access wifi.
just my 2 cents on the concept.