While I also like that comic, this doesn’t exactly happen regularly and no one here ever needs to worry about something like this.
So unless you’re an international spy or some very important whistleblower that won’t happen.
A court could probably order you to decrypt it but again if they have to do that, odds are that you are doing something pretty terrible.
These SD cards are for photographers and normal expandable storage for devices and not state secrets or something highly illegal.
Honestly, neither does having to securely wipe SD card (or any storage device for that matter) as one cross the international border like the thread further up suggests. So the whole thing is just having fun with (potentially roleplaying) over paranoid people :)