Favorite obsolete formats.....

I add a vote for multichannel SACD.

Everything analogue is what I miss. I have a finely tuned and customized Nak 682ZX that I play every other day. I make compilations off vinyl and cds. And I use $2.4k retail interconnects with it. And the very best cassettes - Maxell Metal Vertex. Most people have no idea how cassette deck can sound. No, it's not good R2R or comparable turntable. Biggest problem - you got diminished soundstage, but it's not bad.

KDKA Pittsburgh...AM talk radio. First AM station.  Powered up to 50,000 watts each night. Listening as a kid in bed it was another world. Clear as bell on a good radio, but you could listen with a 5 cent transistor and a few wires. 

I loved MiniDiscs.  I still have a deck and a Walkman.  I copied my CDs so I could play my music in the car.  You didn't need to worry about getting them in a jewel case or having someone break in and steal them.