I tend to get lots of spare cards lying around, heck, there is currently an 8 of spades in my car (on its own) and I just havn't bothered to pick it up yet. Since I only use Bike and Bee decks, I just stick em ontop of the deck and force it.
Also, after conventions I end up with a lot. Reason: I carry a dck around with me, and when I meet a lecturer or other famous magician I'll ask them to autograph a card. At blackpool I got 12 cards autographed. The remaining 40 are now in my signing pile.