We've never had much of a formal policy with our nanny (live out) about food, in general, it's understood that she can eat from our stuff, although we sometimes say certain things are off-limits. She tends to diet a lot, and so doesn't really make much difference
. It has bugged me occasionally though that she will buy M&S salads from the kitty purse when there are all the required bits to make a salad in the fridge, but we haven't got round to saying anything about it. And the yoghurt I buy never seems quite right for her, either 
Today she sent a text to complain that the kitty was empty, and what was she to do (and I was aware that she was expecting a playdate in the afternoon). My response was that there was lots of food in the house and in the freezer, which there was. Seems she didn't get that, she went to Waitrose and spent £11 on various bits, including about half on food (including prawns) which was clearly for her and her nanny friend....seems a bit OTT to me, but not sure what to say or how to say it. 
I suppose it's all a bit of a give and take, she will often eat elsewhere on playdates and not here, but I was still taken aback.
Any thoughts?