Found laptops on the street fully abused and often smashed to bits. Recently pulled a 160gb SSD out of one. That’s worth keeping, as well as the RAM, often.
TV tuners/media players: they sometimes have internal hard drives. I recently pulled a 320gb 2½″ HDD out of one. Even though that’s likely too small to serve as someone’s laptop system, anything bigger than 120gb is big enough to store a copy of the whole Debian system including all apps (5 blu-rays merged these days).
All DC powered electronics: it’s useful to cannabalize the female barrel connector. There are many universal PSUs with a collection of male tips, but never female tips. The female tips are useful for making your own barrel adapters, instead of cutting and soldering your OEM PSUs.
SSDs, even 120gb ones, are definitely useful in this day and age. A year ago you could just buy a brand name 120 or 500 gb SSD for cheap for throwing into an old PC. Now a days a new 500gb SATA Samsung SSD is $274 CAD.
Yeah, you can buy a cheap USB-to-SATA boards/cables (or enclosure) and use them as USB drives. I have an rPi booting off an old SATA-HDD (more durable than micro-sd in my experience). Unraid supports arrays with mixed sized disks too, so you could make a NAS.