We had our au pair open a bank account to make it easier to pay her by check.  The bank has one of those "you must take money out at least 5x per month" policies if you don't want to get charged the $6/mo service fee.  She doesn't spend a lot of money, so she figured that she'd use her bank card for meals when outside the house for class.  On the evenings our au pair had class (M/W 5:30p-9:30p), she charged her dinner to her bank card over at school.  She submitted these receipts to me for reimbursement since she wasn't at home for dinner. 
 
I checked with our local coordinator, and learned that the au pair is responsible for meals outside the home (unless you are taking the family out to dinner - In that case you should pony up and pay for her too as part of the family).  That saved me $12/week!!