My mums wallet got stolen out her bag in a bus line, in London.
She obviously had to cancel her accounts. Her accounts are joint with dads. It was horrible, we spent a week of our big holiday on the phone to the banks, trying to get money sent over for us. We got emergentcy cards sent over, and they didnt even work, because London didnt accept then. (But Hydra a small greek island did! get that!) They amount of money we spent calling from mobiles is crazy.
Lucky we had family over there, so they lent us money for the time being. But my parents keep saying, the wouldnt know what someone would do, if they didnt have any family over there.
So words of advice, when travelling, have seperate bank accounts