I use external USB drives. And still I would advice you against offline storage. When I was charged with the "hate speech" crime in Russia, all my laptops, phones, storage device and paper notes were confiscated as "the tool of the crime". Except for a single USB drive (fortunately having all my backup source code), which was hidden and wasn't found during the search by lazy FSB operatives. Also, if cops find any password protected files, they will likely apply torture to you until you tell them the password.
Since one of the confiscated textbooks had online passwords written in, I had to change all my passwords for all sites or create new accounts. You may ask how did I managed to evade the jail and left Russia in a single piece? Using bribery obviously. But it was just impossible to bribe them into getting back my computing devices.
So yeah, it is a good idea to learn the usage of anonymous online storage services. Steganography in addition to encryption wont hurt either. Some people suggested uploading a popular porn movie with your data hidden inside into the ed2k network. Then it will persist until the extinction of humanity
Then again, if they kill you in prison or during interrogation, you wont need your data afterwards
Everything is temporary in this World, so a Buddhist approach of not holding to the things could also work well.
You probably think that it will never happen to you, because you have no problems with police. But they may charge you by mistake or if your room mate or relative gets in trouble with government - they will confiscate all devices in the vicinity, without asking about ownership. Then there are such things like fires and floods.
IIRC, all storage and trust services are required by law to be non-anoymous. But you can still hide your storage device in some forest. Just watch for forest guards. If they find you hiding something, they will call police outright.