I have never hiked the Appalachian Trail. But somewhere I read advice for what "through-hikers" should carry in their backpacks, and I have used this advice to pack for various trips.
The advice, as I recall, is this:
Make three piles of gear:
- Items you definitely need and cannot do without.
- Items you might need, but could likely do without.
- Items you definitely do not need, but would like to have along (e.g., guitar, camera, or frisbee).
- Take half of the items from the first pile;
- none of the items from the second pile;
- and one item from the third pile.
[Title refers to this. If you know the original source of the advice I recapitulate above, please let me know!]