The idea of walking, potentially, several miles carrying plastic grocery bags with enough stuff to last a week for 3 doesn't sound goos to me.

Shopping at a grocery store when you are tired doesn't sound good compared to picking up a box that takes 5 minutes.

We want a daypack for while we are on the trail, and the little Osprey Daylite seems ideal for what it is, but certainly not enough alone for what I'm considering.

Going to the store would likely be for anything we didn't have the foresight to consider, or that we found what we packed wasn't quite enough, or that something was broken or lost, and quite possibly for craft beer or wine to enjoy back in our room while we relax.

I'm curious why people would regret sending themselves boxes? Or is it that they often send too much stuff?

I've been trying to find maps of the AT with the trailheads that head into towns so I can get a better idea of distances and towns to stop in, but it doesn't seem to be quite that detailed.