Theres a huge variety of drinks available in Japan and you could last quite a while drinking something different every day.
When I lived in the UK, I would miss drinking Calpis Water after trying it on each trip I made to Japan - not sure if its widely available over there now. I believe this drink was renamed Calpico because "Calpis" sounded too much like "Cow Piss."
Now that I live here, I miss drinking root beer which I could pick up in Tescos - its not widely available here and I need to drive about 40 mins to Costco to get some.
One of my fave all time drinks is Sarsi - a drink widely available in Malaysia which also tastes a bit like Root Beer.
One think I found interesting about Japanese culture is that Tofu milk is not a popular beverage even though Tofu is widely used in dishes. The Tofu milk in Malaysia is just fantastic - do try some when you are over there.
Photos of vending machines and drinks follows. You will notice that there are some freebies attached to some drinks at no extra cost. Some are useful, some make you want to hit somebody. The One Piece freebie attached to the Fanta is a refrigerator magnet which also seals bags of crisps - left it in the hotel bin ^^;
The vending machines over here are brightly colored - the ones in the UK were huge black metal boxes with a Coca Cola logo - I'm guessing its to prevent people taking the whole machine home with them ^^;
Hmmm, come to think of it, I didn't notice many vending machines when I lived in Seattle.