Given that Thoreau's core lesson was "simplify," I admit it's kinda weird that Walden Pond has a Thoreau gift shop: I mean, if you read Walden and then want nothing more than a souvenir Thoreau bottlecap opener, to accompany the bottlecap openers you already have, then it's probably fair to say you missed the point :)
If I were managing that gift shop, then just to make the point the gift shop would carry only one item: paperback copies of Walden. There wouldn't even be alternate editions. In fact, at that point I suppose the gift shop wouldn't even need a normal cash register: the cash register could just have one big button that says "Book."
Or, better yet, get the books in bulk and dispense them on the honor system for a suggested donation.
Then the "cash register" wouldn't even need that one button. In fact, you could skip it entirely.