Ed - I always enjoy going to the basement level of large department stores where there is a large selection of individual shops selling food. The variety is incredible and typically there are some things there that you probably haven't seen before. That is also typically where tea is sold. There are usually one or two teashops. Sometimes, like during shincha season, they give out samples. I also like to go to the housewares section to check out teapots and other Japanese pottery/dishes/etc. There are several large department stores in the Ginza and Shinjuku sections of Tokyo. You can go to Takashimaya, Isetan, Mitsukoshi, etc.
I also like to find places that sell Japanese sweets, both mochi type things and iced desserts that contain matcha.