This is a term we're going to have to explain to the younger generation: when games were shipped in boxes, those contained at minimum a disc and a printed manual, but some companies came up with gimmick items you could put in the box and "feel", to enhance your immersion in the game.
I still have my Ultima 6 "moonstone" and cloth map somewhere.
A lot of the original packaging could be rather unique generally but eventually they ended up standardizing for retail shelving.
I actually think it gives a lot of immersion than modern day AAA games.
https://www.iam8bit.com/collections/collectors-editions/prod...
Now, for many of us, they are prohibitively expensive, but they are available.
Trinity is another good one. As is The Lurking Horror--set at a thinly-veiled MIT campus where many of the authors were from.
Zork is by far the most well known, but also pretty infamous are Hitchhiker's Guide to the Galaxy, Leather Godesses' of Phobos and A Mind Forever Voyaging.
As a warm-up, I'd recommend Moonmist. It's a mystery game listed as a "Beginner" game, and is great for introducing elements of the Infocom system.
The feelies are available to view here: https://gallery.guetech.org/greybox.html
There are a collection of game files here: https://eblong.com/infocom/
My preferred player is still Frotz. It compiles and runs on practically anything, my Psion, my Pis, Windows, everything.
https://gitlab.com/DavidGriffith/frotz