The answer for most people is almost always "Not enough." The best method is of course to automatically back up your devices either on to backup hardware, partitions, external devices or servers.
I do not do such a thing, however. If my data was crucial to my work or if I've invested untold hours into a serious personal project or something, I would. But as it is I only stand to lose bookmarks, hundreds of accumulated image files, hundreds of hours of saved games the latter of which are backed up to cloud storage via their digital distribution platform services (Steam and GoG).
Also, I don't trust cloud storage services. I will simply never entrust my data to a third party or anyone else who could have access to that third party. I want my data to fit in my lap, so to speak, in a device I can hold in my hand, not some random anonymous server lost in some warehouse in Timbuktu.
But every once in a while I will manually copy image files and word documents to external thumb drives. It's not the most elegant solution and it doesn't work if there's a failure before I bother to get around to it.
My laptop is getting long in the tooth and I keep expecting a failure any day now but it keeps holding out so far.