There is a lot of material on WhiteBlaze, a forum specifically for Appalachian Trail thru-hikers.

You'll be passing through lots of towns with laundry facilities, so you certainly won't be wearing the same clothes without washing for six months! Not only is there no need to take so many changes of clothing, but you are setting yourself up for injury by carrying an unnecessarily heavy pack.
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May your trails be crooked, winding, lonesome, dangerous, leading to the most amazing view--E. Abbey