I have been using a computer since the early 80s and have data stretching back that far so I care about this! I use Apple so Macs, iPhones and iPad but the principles are the same whatever you use. First line is the cloud - it's surprising how complete this feels when you get a new device and all your calendar entries, contacts, photos etc magically appear. Also on (in?) the cloud are documents in DropBox. Second is an external hard drive plugged into the Mac and using Time Machine to do continuous incremental backups. It's great to be able to wind back a day, a week, six months - whatever. I imagine you can get something similar for most OSs. Lastly, I keep another external hard drive at work. Once a week I bring it home, run a backup and return. I learnt that lesson after the house was broken into and the computer and everything connected got stolen (although back then I did have a backup on hundreds of floppy disks!)