Beer. Not to show, just to enjoy it.

my laptop so i can show off gnome and emacs (and my trackball!)

If we could go outdoors I could probably bring my bootleg pelican case full of ham radio equipment, deploy an HF station and try making some contacts while explaining how each of the parts works

I play Warhammer and D&D...and have extensive mini collections. I'm envisioning a diorama.

Or a few of my favorite knives and a good whetstone, to show how easy it is to do and teach a good skill!

I'm an antenna engineer. I'd bring an antenna because after hearing a lot of adult show-and-tells I figure people could probably use some sleep.

I own a sextant. I have other cool stuff, but that's the one that probably has the most universal appeal.

This has been a very cool thread.

I'd like to bring a tall ship sailor. Preferably from the 18th or 19th century. I bet they'd have some interesting work stories to tell.

I'd bring my Split ergonomic keyboards I've built/am working on.

I'd love to get others into the hobby or crowd source help in coding QMK from those who are already in it. Online forums are a great resource but for some there's no replacing an in-person teacher.

I'll hopefully come back and edit this post when I get home to share a picture.