Coffee is really tasty!! (Japanese word for tasty is "oishii"). But you will often get a smaller cup than you expect. In restaurants, it is served in a tea-cup sized cup, not a North American mug. Even when ordering a large take-out coffee in some cafe's, they will not fill up the paper cup. They will leave a considerable space at the top (more than just for you to add cream). Starbucks, on the other hand, operates the same as in North America, but a little more expensive. Also, in most restaurants, they usually charge you per cup (i.e. no refill), even if you buy a meal! So just ask if refills are OK. Coffee no okawari wa muryou desuka? Now in Japan you have convenient access to great coffee from vending machines.
The best way to drink Japanese grean tea is to buy a bottled green tea for 150yen. You will find more than 30 kinds of bottled grean teas at a kiosk of train staion or convinient stores. They have a hot bottled grean tea, which would be great for cold winter.