op, I'm not sure if you mean food budget at the parks for a week or in real life for a week.
DH and I budget $100 per day, per person at WDW - buying all meals, snacks, water, etc. We go in May and I can easily spend $30 a day buying bottled water at the park - I basically always have a water, as I soon as I finish one, I buy another. Of course, some days we eat all counter service and don't spend the entire amount - some days we have reservations and can spend $50 each on dinner alone...just depends....
I prefer to overbudget rather than find myself short - so for us $100 per day is good number and we use that to plan our budget for each trip.