Great to see all these supportive and informative posts!
One note. It's quite true that Harpers Ferry does not have a grocery store. But that does not mean there is no resupply. The Outfitter at Harpers Ferry (in lower town) stocks quite a few items for hikers (not all of which are on display, sometimes they have things like bagels and cheese that you have to ask for). Early in the season there many not be as many items stocked as in the peak of the season, but you can always get basic backpacker food items.
During 2017, the Teahorse Hostel started carrying some resupply items for hikers; don't know the plans for 2018. The Teahorse Hostel is closed for the winter (until March). Of course, the prices in these small businesses can't compete with the big box stores (a Walmart is 5 miles west of ATC, available by EPTA bus which runs Mon-Fri, $2.50 each way, several times a day). There is also a 7-11 convenience store 1 mile west of ATC. And the Town's Inn has a sundry shop with some food items and cafe; they're open 7 days a week year round, even when everything else in lower town is shuttered in the dead of winter.
Both the Harpers Ferry Post Office and ATC HQ hold packages for hikers.