1. Peanuts Monaka (ピーナッツ最中）
Monaka is a Japanese sweet made of two thin crispy rice cakes sandwiching mushed up azuki beans. This monaka is shaped like a real peanut, filled with peanut butter based azuki bean jam.
The box is a reasonable size to carry around. You can get one either in terminal 1 or terminal 2.
2. Take Baum (竹バウム）
Take is a Japanese word meaning "bamboo" and baum is a shorten word of baumkuchen. This sweet is a baumkuchen, which is a German spit cake. The unique part of this food is that the shape of it looks like a bamboo tree, and has matcha taste.
You can enjoy this sweet with Japanese tea, English tea, coffee, etc. The taste of matcha will go well with any drink.
You can buy this one on the 4th floor of the main building, Terminal 2.
3. Tokyo Banana (東京ばな奈）
There is no doubt that Tokyo Banana is one of the most famous souvenirs to buy in Tokyo. There are variety of flavors, so it is a good idea to find your favorite one.
As the name explains already, the custard cream in this banana-shaped pound cake tastes like bananas.
You can get this sweet at many places in terminal 1 and 2.
4. Meika Hiyoko (銘菓ひよ子）
Hiyoko means "baby chicken". This is called hiyoko because of the appearance this sweet has. It looks exactly like a chick!
Inside hiyoko is a egg based jam that tastes like custard cream, covered with a baby chicken shaped layer.
This sweet is available at Terminal 2.
5. Koukyo Gaien Dorayaki (皇居外苑どら焼き）
This stuff is a great souvenir for someone who loves Japan. This is a Japanese sweet dorayaki, azuki bean jam stuffed in between two small pancakes.
The unique part of this sweet is that it has a Japanese emperor's family crest engraved on it just like the picture above.
You can get it at terminal 2.
At the end...
If you have a hard time buying a souvenir, these are some of the great souvenir sweets to buy back from Japan. They are all light and convenience.
Also, if you are hungry and want to grab some Japanese food to eat before you leave, you can check these two articles out to find a great restaurant.