Honestly, if you don't have massive amounts of stuff to backup, a microSD might be the perfect solution. Like a 128GB card (normally used for digital cameras). Bury it in a can in the yard and update it a couple times a year. Let a family member know where it is too. Good for document scans, photos, etc.

Secondary advantage: MicroSD by itself is already fully immune to even the worst of the worst EMP events, because it's so f%$^ing small that sufficient current can induct.