For anyone in Japan who doesn't already know and people coming to Japan in the winter there are now a bunch of no frills airlines that can take you from Osaka or Tokyo (or other places if you change flights) up to Hokkaido.
If you book in advance it can be super cheap (less than 10000 return).
Its a 1 hour flight so I don't want food or anything else personally. Just bring water and a snack, in Japan they won't take away your water on an internal flight.
Peach | Peach
There are lots more if you search around.