I rarely carry cash anymore, much less coins, but I found out that this can be a bad thing occasionally.  I recently had to go to the Fasi Building and parked in the underground structure where all parking is metered.  The meters take cards, so I stuck my card in but for whatever reason, it was denying the card.  It might have been just that meter, but parking was tight that day, and I couldn't just move stalls.  I had no coins on me.  Thankfully, another person was coming to his car, so I asked if he had coins to trade for bills and luckily, he did.  Funny thing was, I went to the security office close by, and they don't give change.  Their suggestion was to go into the building where they have a convenience store, purchase something (after waiting in line for ID check, then waiting in line again to exit), then get change....assuming that no one will come by to ticket my car for an expired meter in the mean time.  Lesson learned:  carry 8-12 quarters in the car at all times!