My home-owner perspective - I think it’s rude, mean and inconsiderate to not leave the sitter enough household/pet supplies to last the duration of a sit less than 3 weeks. Longer sits might be different but at the very least I’d leave money to pay for any pet supplies.
For food, I literally mean ‘help yourself’ to anything edible/quaffable 
I just ask that there’s coffee/milk/cereal for my return and to let me know of anything that’s finished, as I’ll arrange for a food delivery the day after my return.