Gee,, all these times I went to Europe without American money for emergencies, , just keeping a cushion of about 200 euros in cash in my moneybelt or safe.. hmmm...
Why bring foreign currency for emergencies.. since you would need a bank willing to exchange it,, and it would not be accepted everywhere in emergency anyways( for instance, you are at a gas station in the country side in Italy,, they want a card, if your card doesn't work,, offering someone euros is going to be way easier then offering "play money" to a stranger to help you out.
Once my card would not work at a train station in France, a couple helped me by buying my ticket on their CC card, but I paid them the cash in euros,, bet they wouldn't have wanted to help me if I only could offer Canadian money..