Yes, eating at McDonald's is bad for you, but if you do eat there on occasion, or even get a fountain drink, you may end up with those little Monopoly stickers.
You know that only a tiny number of them are the rare ones, so you needn't save 10,000 common ones. But to avoid any hassle, check this Wikipedia entry, which purports to list all the rare ones. If you don't have one of those, you can probably just pitch the others.
Even in the early days of the Net, it used to crack me up how people would post saying things like "I have Park Place, looking for someone who has Boardwalk to share the winnings." Um, there are a million Park Places, dude, and one Boardwalk. Like the person who had BW wouldn't just keep going to McDonald's (or digging in the trash) until they also got Park Place? Why would they share with you when they had the lottery ticket and you had nothin'?
I must make the point here that Wikipedia has been known to be wrong, so don't blame me if you pitch a piece based on their say-so that turns out to be the million-dollar winner. But I bet that's unlikely.
The entry offers an interesting read, too, since it talks about how they discovered fraud in the contest in 2001 -- the promotion company's CHIEF OF SECURITY was stealing the rare pieces and passing them out to friends who would share the money. Apparently they'd been doing this for years with all McD contests and made $24 million.
It gets weirder: A widow of one of the "winners" sued to keep receiving the alleged winnings.