Shakespeare’s lost plays: Shakespeare's plays - Wikipedia
A live triceratops.
All those missing Silent Films, lost perhaps forever.

Whatever was the “original” Bowie knife. Many versions are purported to be that piece, but I want the undisputed original one. There are at least these candidates:
(see all the ones below at http://www.relentlessknives.com/BowieHistory.html) and there may be even others.
But there has to be at least ONE original one!
My first wish was the Ark of the Covenant but since that is taken, I’ll go with the missing 17 minutes of the Watergate tapes.
There’s not a specific copy I want but I would love to have an original velocipede and an original high-wheeler, both in mint condition.
I would also love to high some original Black Sabbath sheet music.
As a card collector, I want the first one… something like this
The second half of “Dead Souls,” most of which Gogol burned before it was published.
The missing 007 DB5.
The Gospel of Q
http://www.earlychristianwritings.com/q.html
I want whatever was really in the chamber under the Sphinx. Even just to see it, or know what it is.
Dammit, I came in here to dibs those!
Can I come over and gaze at them?
Is that a lost treasure? I saw it in person, when the King Tut museum exhibition came through San Francisco. In fact, I was fortunate enough to see it twice. (once at school, and once with my family.) I was so stricken with that particular figure that I bought a postcard of it in the museum shop. I remember her eyeliner had a little chunk missing out of it, I finally fixed it on the postcard, didn’t seem right that she should have to go through history that way. I kept the postcard over my altar for years.
Dang! I forgot about the Amber Room - are you willing to break off a little piece for me? Maybe just a closet?
The Storm on the Sea of Galilee by Rembrant.
Another one is most of the gold and jewels that was lost in the Noche Triste when Cortez’ men escaped from the Aztec capital. In their greed many Spaniards were reported to drown in the now buried water ways of the Aztec capital because their bags and spaces in their clothing or armor were stuffed with gold. So several places under Mexico city could have a grim bonanza.
And speaking of more possible buried gold: the lost Inca city of Paititi, thanks to modern technology and recent explorations there are hints that this one may be close to being identified/found in a few years.
Hitler’s Ball.
The library of Alexandria.