On any given street it is possible to find as many as seven or eight "Konbini" - the Japanese version of a convenience store. You can always depend upon having one very close by. Just standing on the street where I live, I can see three! Compared to the convenience stores that I am used to, these are very different. They have the same function of providing quick, cheap food and supplies; but with quite different things being offered. I know of at least four different "Konbini" companies that can supply anyone with a quick can of coffee or a cheap "Onigiri" (riceballs) in Tokyo.
Japan has taken the best of the convenience store idea and adapted it to Japanese expectations. There are things like Calpis (a sweet milky white drink that you have to try to understand!), Japanese bread (which is often stuffed with strawberry paste, chocolate, or custard; and is always sold in a single serving), and fresh sushi all in the same place! The store workers are almost always polite and welcoming, even when you go to buy ice cream at one in the morning.
I have even been fortunate enough to find convenience stores on the first floor of office buildings or tucked away in a quiet residential neighborhood-where it would seem rare to find such a thing. They are everywhere! Compared to the many convenience stores I have visited in the most modern countries in the world Japan's are much more reliable and interesting.
It is also interesting to notice that because so many people don't own cars in Japan, there are many convenience stores that don't necessarily have gas pumps attached to them. This allows for many more convenience stores to be designed with more of a focus on food. With the dense population of Tokyo there are many more people walking than driving and the ratio of motor vehicles to gas stations is represented as is the ratio of convenience stores to people walking around in the street. The best thing about this is that there is more room for the delicious.