My plans for my US trip earlier this month included a lot of shopping. With two suitcases plus two carry-on bags, I had a lot of space to carry snacks and cravings back. But I had heard a lot about National Azabu, a supermarket near Roppongi which carries lots of imported foods and ingredients.
National Azabu is a good choice for those looking for ingredients and foods that aren't part of Japanese diets. But I still haven't found a reliable source of candy and snacks. Upstairs is a selection of household goods - toilet paper, cleaning supplies, etc, cookware, and English-language books.