As dumb/simple/boring as this may be…? An external hard drive.
…
…what? It doesn’t require you to be online 24/7, works at any™ PC, and the speed is really great – even on a potato.
Unless you work at NASA or at IBM or similars – then feel free to call me dum.
Eh…you’ve got a point there. Then again, there is always pendrives and other extremely small devices where you can copy your (mostly important/crucial) files in and carry it along with your house/car keys or something like that.