I can only answer from memory but...
It snows in Tokyo about as regularly as it does in London, so not a lot, as in London for it to snow on christmas is just luck
In order of what I've seen the most:
Drinks, Cigarettes, Food, then other assorted things like porn, magazines, etc
If you're in Tokyo, the local game shops are just as good as ones in central London (maybe smaller and less flashy, but the selection is still good).
Sushi is better in Japan than anywhere else in the world, as far as I'm aware, lol. But forget the taste for a second, its a HELL of a lot CHEAPER as well
I'm afraid I have no idea on the last one, lol.