This guide to how to prepare for a Thru Hike is one of the best I have seen, except for one chapter, Chapter 5, Getting Your Gear On, The Pack.
Little is more important than sellecting a good pack. The author does not fairly state the advantages and disavantages between internal and external packs. To say that the external frame pack was used mainly between the 50's and the 70's on the AT is totally misleading and incorrect. External frame packs have been the backbone of hiking the AT. They still should be considered, when choosing a good durable, sturdy, highly useable, yet comfortable pack for a thruhike.
For good reading, to help you select the best pack for your Tru Hike, I would recomend, Long Distant Hiking, Lessons from the AT by Roland Mueser, Backpacker & Hiker's Handbook by William Kemsley Jr. or The Appalachian Trail Hiker by Victoria and Frank Logue,
After becoming well informed, go to a GOOD pack shop and try on the various packs you read about. Don't be pressured into buying the pack that the salesperson is currently pushing. Know for your self what to look for in a good pack and why. Your salesperson may be into the current fad of Ultra Lite Backpacking, but is a super lite, one large pocket frameless pack, your best choice for a tru hike?.
The rest of the book is very well written and I recomend it highly.