One thing about a week walk that is generally different than longer walks is that most people probably start out with a good supply of stored energy. I know I carry a nice 5 lb energy packet with me at all times. If I am doing 10 miles or less per day, under 1.5 lbs per day works well for me for 3 or 4 days. By the 4th day I have somewhat depleted those stores and am a little hungry if I am only eating about 1 lb per day. If I am doing a regular 13 miles or over per day, I am into the "needing more energy every day from the start" zone. In other words, if I don't eat enough food each day, I will pay the next day with a lack of energy.