i've been collecting flyers from events my sons produce or play at and will one day use them in a large piece of collage.
i live in a small town and sooner or later, almost everyone gets their pic in the paper, ao i've got clippings of pics of my kids when they were young that i need to do something with. those are my faves.
those psters your friend found sound amazing. i saw an antiques roadshow recently where a woman brought in a poster for a SF bob dylan concert (admssion $2!) that brownie mcgee had written a song on the back of. worth $5,000.

Wow...I have so much that it's really hard to choose. I really am proud of my vintage Hal Roach Studios letterhead. I was a big fan of The Little Rascals and Laurel & Hardy when I was younger, so it just seems cool to have this. I have tons of old sheet music, cigarette cards, postcards over 100 years old...it's tough to pick just one thing. Oh, and I can't forget my 3 Godzilla movie posters from Thailand...those are pretty damned sweet too.

1942 Lick Wilmerding High School Yearbook. Strange, rusty spiral binding. Every page is a treasure. Came with a 8x10 magazine 2-color print of Judy Garland stuck inside it (before she was a gay icon.)

Once Bought an old green trunk for twenty bucks, just to go through it. It was full of postcards some going back to the fifties, souvenirs from japan and around the world, and a red cross badge a a pouch of ration stamps with some tokens along with other odd stuff. Looked like sombody stored the trunk in moms house and mom periodicaly stored more stuff in it or something. My favorite one is a student news publication 'The Bell'. Published by San Jose High School, 1903.