You can have Uniq Japanese original flavor coke in Japan!
I think it's good souvenirs for friends or family in your country
Pepsi Japan sells Pepsi Azuki (red beans) flavor coke and Shiso (Japanese basil) flavor coke.
Coka Cola Japan sells Coca-cola plus Fiber & Coca-cola plus which has Vitamin C.
These coke sell only in Japan, so it's good souvenirs