One good way to keep food expenses lower for those on a tight budget is buy food for a picnic lunch every day at one of the well-stocked grocery stores (SuperValu is a great example, their fresh bread and pastries are excellent).

Lidl & Aldi stores are by far the cheapest for food purchases & also usually do fresh breads, pastries, etc

Do bring plastic cutlery in your luggage (for yogurt) and possibly even an insulated lunch bag like those that REI sells.