Now that I don't live with roommates anymore, I'm past the days of labeling my food
We don't have a ft nanny anymore, but we have temps a few times a year and always tell them to help themselves. They have all followed what I consider normal common sense. None have finished off anything, or cooked stuff fr scratch out of the freezer, or finished off leftovers.
When we had a ft nanny, she generally brought her own lunch and just had snacks or drinks from our stuff. She was welcome, and did, put stuff on our grocery list. But that was just for extra stuff as we just bought it at our next weekly trip.