I own a comic book crossover between the Punisher and the Batman(the Jean Paul Valley version of Batman, not Wayne). The book is not as famous as the Punisher's other more well known crossover with the mainstream Wayne Batman but I like it.
What is the rarest thing you own?
A Flyers cap signed by the entire team from the '74-'75 season, when they won the Stanley Cup.
1 Brazilian Real (banknote). They stopped making these several years ago and substituted them for 1 Brazilian Real coins... I'd say it's useless, even though I still have about three of them. They're pretty darn rare now.
Manners. Seems rare to have those in today's world.
My Uncle Antone's helmet and tunic from his uniform from World War One. I keep them in pristine shape and perfectly preserved. I even have an old picture on my wall that he had made into a portrait when he was in France in 1918. It's a really nice heirloom.
A flag from a World War two German U boat
My wife and I have in our possession a 2,000-3,000 year old coin.
I'm going to be rich with this lot one day. ..
I have some of the first commercial radios made, old coins (foreign and domestic), recordings on wax drums, paper records, 78 rpm records and so on. Some are supposedly quite valuable.
The rarest things I own however are the items that my family have given to me or made for me over the years. Birthday cards with written notes, school projects, and other things they took the time to personalize or make outright for me.
The 'valuable rare' items I have are becoming more and more things as I get older. The items that were given and made by family are becoming the really valuable and precious rare items to me for the memories they evoke and other intangibles.
You could own the Mona Lisa, a unique painting, and yes, rare. It may bring you pleasure to say you have it, show it to friends and know its worth lots and lots of money. But nothing is rarer or more valuable then a crayon drawing given to you because you got rid of the monster under the bed or held her when the thunder was too loud.
Don't confuse rare with valuable, sometimes rare isn't valuable to anyone except the owner. You could end up like Orson Wells in 'Citizen Kane' surrounded by rare valuable items to everyone else, but wanting a rare item only really valuable to him at the end.