The best shopping to be found is in the Nakamise. Nakamise litterary means something like "shops inside". You will easily find the Nakamise just past the Kaminarimon Gate. There are many stalls where you get something to eat like rice crackers or cakes and the area always looks like it is celebrating some sort of a festival.

This is a good place to shop for souvenirs for your friends.  In Japanese culture, gift-giving is an important ritual that showcases your thoughtfulness and esteem for the person.  That's one reason why they will always buy small souvenirs for their colleagues when they travel.