Drop a thumb stick (mechanical failure) into a plastic zip-lock in a vacuum (oxygen) then into a metal thermos mug with water (pressure and radiation) then dig it really deep (accidential discovery and weather). By the time it deteriorates you’d have problems finding USB interfaces to plug it in. The location itself is largely irrelevant, but I’d recommend some place far from human-occupied places.

The authoritarian state problem isn’t solveable, but you can defend it by obscurity, like not leaving a trace of thinking about this info cache, or leaving too many of these caches to reliably dig up all of them.