In his "Music in the Round" column in this issue, Kal Rubinson nails it: "An accessory is something without which your system would still work just fine." Thus, unless you're one of those Neanderthals who assign to audio cables (footnote 1) that rather dubious distinction, there isn't a single audio accessory on the planet that anyone actually needs (footnote 2).
But because most of my listening is to LPs, I find that a reliably good record-cleaning machine comes closer than any other accessory to being essential to my full enjoyment of…