What is the most "rare" game-related item you own?

I had to sell a majority of my old/good stuff some years ago during a lean time, but managed to keep a couple goodies:

Panzer Dragoon Saga (orig. US release, preordered that sucka)

Guardian Heroes (US release)

I've also still got Guardian Heroes JPN release, but that's not nearly as rare as the US one afaik.

I still sorely miss most of my Saturn collection, but haven't had the heart or the cash to rebuild it.

My stuff isn't that rare, but stuff that's can be a bit difficult to get a hold off.

PAL PS2 versions of Digital Devil Saga 1 and 2, Nocturne, Killer7 and Shadow of the Colossus. Oh, and Persona 4 I guess. The SMT games are big for me to own, especially since the selection of PS2 and PS1 games on PSN Australia is pretty bad compared to NA. Still have a few quality titles, such as MGS and Silent Hill, but of the SMT games, we only have P3 FES for some reason.

Oh, and the Japanese Persona 3 soundtrack, which basically has every single track from the game (it was a pleasant surprise too, as I thought what I had purchased was the NA soundtrack that only had some of the major tracks on it. Instead it's about 50 tracks, including sheet music for Battle For Everyone's Souls. Pretty neat).

Not sure how rare it is but I still have an original Diablo disc and case for the PS1. I don't recall seeing many of those around.

Most of my rare stuff is comic book related.

I don't get too into the super rare stuff, so the rarest thing I have is probably Rockman & Forte (Megaman & Bass) for the Wonderswan. It's not a great game.

I have a combo Mario 1/Duck hunt cartridge - I think I heard that was rare?

I think the rarest game I own is a copy of Snow Bros for the NES

I had a Gizmondo. My rich aunt gave it to me for Christmas many years ago. Apparently the guy at the mall kiosk convinced her it was the hot new thing. Unfortunately I lost it many years ago. It's probably in a box in my parents basement.

An original copy of Earthbound with the box and player's guide in acceptable condition.

Up until about a year and a half ago I had been holding onto a prototype version of NES Ninja Gaiden since the mid 90's. Sold it last year since I had no emotional attachment to it (even though NG 1 & 2 have the best NES music) and got like 850 bucks for it. No regrets, would rather have the money.

Zelda Game & Watch that I got from a drawing competion that was on a side of a cereal box

I've got some Pogs laying around...

Hrmmm... Every major system release since the 2600? I still have my box for the NES, SNES, 64, PS2, and XBONE. There is the fact that I still have the boxes, instruction manuals, and extra shit from when I was a kid (like Chrono Triggers maps and posters, or Earthbounds Strategy Guide pack in).

Other than actual games though, I stay away from related gaming merchandise. I have a feeling that collectables are going to be worth nothing in the future because of advances in 3D printing or digital rereleases of older games.

Let's see. I have a complete copy of Marvel Vs. Capcom 2 for the original Xbox. It's opened but I only played it like a half dozen times. Talk about one of my biggest regrets. I really should of just kept it shut.

I have a mint condition, complete big box copy of Daggerfall. I don't know how rare that is but it goes for up to $50 on eBay so I guess it is at least a little rare.

I have a beat up but working Gamegear as well as a handful of games for it.

I have a bunch of other older PC games complete and some in mint condition but I'm not sure how valuable any of them are.

And I have a sealed copy of Tactics Ogre PSP including the tarot cards which goes for something like $40 on eBay.