The tour following American Idiot in 2004 and 2005 was massive. It consisted of 161 shows, to be exact. More shows means more equipment, and more equipment means more guitar picks. Billie Joe typically has a mic stand stocked with around 10 guitar picks at the beginning of each show. Some of these are thrown into the crowd, picked up by stage hands, or lost into oblivion. And, sometimes, they reappear on eBay.
If you've ever wanted to own a guitar pick that was actually used on stage by Billie Joe, we've got three chances for you (Auction 1, Auction 2, Auction 3). All of these auctions are for American Idiot tour guitar picks (black with red print) that have the heart grenade design on one side, and the band's logo on the other. These picks weren't ever and won't ever be available to buy anywhere, so eBay is your best chance. Two of these auctions are a bit pricey, but use the "Best Offer" option to get a better deal.