How do you decide which papers to keep or to shred?

I'm having a proper clear out. Or trying anyway. Have realised that two shelves of A4 folders of paperwork is probably not strictly necessary. But how do you decide what's worth keeping and what's not worth the space? Of course I have most of my accounts online these days but what happens if I pop my clogs suddenly and no one knows how to access any of my accounts? Or that they exist?