Found in the mix of shops and connected buildings in Tokyo station, Daimaru has a variety of food and retail shopping sections (https://goo.gl/maps/oYCH8).
The basement level is where the food stuffs are – fresh food, pre-marinated food, packed food (bento, etc), food gifts, coffees, chocs, and much more.
There is also a Kit Kat shop in Daimaru where you can get your hands on the only-in-Japan variations.
And as usual, all cute things are found in Japan, here’s some gift food.
Daimaru is interconnected to many other shops and areas of Tokyo station, so be sure to check it out when you are in the area!