What's the rarest or most unusual computer-related item do you own?

[Terry Stewart]

It would have to be the Polycorp Ploy 1, I obtained recently.

http://www.classic-computers.org.nz/blog/2016-10-9-poly-acquisition.htm
http://www.classic-computers.org.nz/blog/2017-01-08-second-poly1-fix.htm

This is a New Zealand designed and manufactured computer, and although I
know of a museum display, and a couple of collectors that have one each in
storage, There is one person in another city (Dunedin) who runs the Poly
Archive site. I'm assuming he has a working one (or two).  I suspect his
(if it is working) and mine might be the only verified working ones in New
Zealand, and possibly the world (some were sold to Australia and China).

This Panasonic might not be common..
http://www.classic-computers.org.nz/blog/2013-11-22-playing-with-a-panasonic-jd-850M.htm

..or this Telecom computerphone
http://www.classic-computers.org.nz/collection/computerphone.htm

Regarding the unusual there is this:..the Lang Commander.
http://www.classic-computers.org.nz/blog/2011-12-11-1802-trainer.htm

A kit made by a community college teacher.  He ran night classes on
computing and got students to build their own trainers.

Terry (Tez)