Both GLC and Will D have great answers. I would look into a book by Ray Jardine, he`s pretty much the father of Ultra Light long distance backpacking. His website is excellent, it has great experiences, tips, and produts on it I`d also recommend picking up his book on Long Distance Hiking. I also recommend reading the article on his website about the Cannonballs. RayJardine.com
I`d also recommend getting in touch with someone from the ATC. I believe it is them that sells an AT planning kit. It comes with all the maps you need plus the guide books for different portions of the trail. The books provide info on the post office addresses along the trail as well as places in town just off the trail that will help you stock up. I know of some people who had mailed all the food and gear they would need ahead to the postoffice and if they didnt need it the post office would fwd it to the next postoffice free of charge, as long as you didnt open the package. But I`ve had other friends who got sick of having the meals they mailed to themselves and started stocking provisions from town, this way they got what they wanted and craved instead of being fed whatever you packed a couple weeks if not months ago.
Also, get to a reputable outdoor retail store and ask a million questions and try everything on. Thats what the employees are there for. I`d do some research before you go this way you at least know the terms and the gear you`ll need.