Families are basically always super nice to me and say I can eat whatever I want. Never met someone who told me I couldnt. I do always end up bringing my own food because I'm vegan and because most people don't have the same taste preferences as me, but maybe I'll eat some of their pasta or a piece of they're bread or something. I definitely wouldn't just eat all their food or any of their nice food. I'll also try to eat things I think will go bad before they get back like vegetables because who wants to come home to rotting spinach? There was one nice family who said I could have whatever I want, but did make a box of "sitting snacks" with just random food you might crave in it like cookies and things to make meals. Maybe put what you'd be okay with the sitter eating in a box & say the rest is off limits because you have a party coming up or something and need to keep track of the food?