I have rarely left a show without at least ten to twenty playbills. Remember, they are filled with ads so the sponsors have no problem with that (as opposed to the big pay programs which have none and the show's producers want to sell).
I still to this day will make a loop around some of the theaters when I'm in town and grab all the playbills in the garbage. I find that those who are going to throw their playbills away rarely carry them more than a block.
And why do I do this?
I attended the opening night of "42nd Street" (among others). I left with only about ten because when it was announced that Gower Champion had dies (David Merrick - what a pr**k) people DOVE for the piles of programs at the rear of the audience.
Do you know how much an opening-night-Champion-is-dead program is worth these days?
If you are shopping on ebay, go to the store of Paul Ydstie. His ebay name is Broadway!!! He has the most comprehensive listing on the web. He's not cheap, but he finds amazing stuff and the quality is excellent.