It was real rare for us to hike for more than 3-4 days w/o a resupply. Because the AT runs pretty close to civilization you are never more than a day to a grocery store no matter where you are. It might take some effort to get there, but it is possible.
You may want to reconsider your mail drop schedule as most towns have a full service grocery store. We're talking Supermarkets in most cases. There are indeed a few towns where a mail drop might be helpful. Since this is the case, it is easy to hit a road corssing, hitch into town, hit up the grocery store and pizza joint, and get back on the trail. You can even do this and still get your full day of hiking in.
When choosing food, it hinkt he rule of thumb is 100 calories per ounce. This may or may not cut down your food weight. I used to carry Luna Bars, packets of Tuna, gorp, granola bars, candy candy candy, hot dinners, the works. I just like to eat.
Hope this helps