This is something I have been putting off, too, mainly because the thought of doing it does feel as though you're preparing to jump in your coffin.
It has, however, been at the back of my mind since my husband's spinster aunt died just as my middle son (now 34) was born. My parents-in-law had a heck of a job with the stuff she left.
My FiL was fairly incapacitated by then and my MiL did her best to start clearing out his workshop and the cellar (he had had his own plumbing busness, taken over from his father, and the files of old invoices went back to 1945!)
Unfortunately my DH seems to have inherited the hoarding gene and his workshop is a huge junkshop, and has three of everything - his, his father's and my father's. Not to mention his study which hasn't been touched since he retired. Teaching languages involves tens of thousands of books and they're still all there!
My mother has cleared her home of all books and superfluous stuff and I go through a couple of cuboards every time I go there, throwing out and sorting through. She is happy to get rid of things and only uses a half a dozen things from one week to the next. Books she reads she gets from the library and returns them.