[neilv]

Yeah, this is one of the ways that entire spare units come in. Something on an old workstation breaks, you always have a spare of every part, tested together. (I actually just move the SSD/HDD to the spare, and then worry about repairing dead machine.)

Other than that, I can only guess. PSU and HDD is good idea. If you have an old industrial device that really needs floppies, buy them now, and also be looking into the retrofit options. For laptops, right now I've guessed at stockpiling keyboards, fans (but not the whole heatsink assembly FRU, just the fan part), backlight tubes, display inverter boards, AC adapters, the laptop-side AC adapter connector, HDD caddies and doors (often left out of replacements), upgrades for RAM and for faster/cooler CPUs.