If you pack carefully it is possible to use fresh foods for meals the first day. Many campers drive to their campsites with coolers, and have access to grills. Foods can be prepared in advance, refrigerated or frozen, and packed with a cold source. Freeze water in a plastic jug and wrap it with the frozen foods in a plastic bag, then stuff the bag inside a sleeping bag in your backpack. This way the food will be kept cold while you hike.
Water is always an important consideration on a hiking trip.
You'll need it for preparing foods as well as for washing up. Purchase purification tablets or equipment from camping supply stores, and learn purification techniques. You may wish to bring along some bottled water. Cleanliness is essential. Pack soap for handwashing and dishwashing.