Sapporo is a city in the Hokkaido prefecture Japan.
South towards Hakodate
If your objective is to get out of the Hokkaido prefecture by boat, you will need to get to Hakodate where there is a ferry to Aomori. Going South is fairly easy because of Sapporo's grid-like design, but getting out of the city limits to a highway service station is difficult. The Hokkaido Expressway (Toll Road) is more than 6 km East of the city centre and still in a densely urban region. Highway 36 will also get you going in the right direction. You can get to a service station on at the edge of Sapporo by riding the JR city train to the Minamichitose station Which puts you at the service station situated at the interchange of Highway 36 and Highway 337. Make sure you are hitching at the right exit!
Getting into the Centre of Sapporo is quite difficult. If you don't know where you want to be, it is best to ask to be dropped off in the Chuo-ku ward. This will place you near a lot of the attractions and close to a good selection of cheaper accommodations.
Accommodation and Sleep
As with other major cities in Japan, Sapporo has a handful of Manga/Internet cafes. One of the most widespread is jiqoo. Becoming a member is cheap (~300 Yen) and you can rent a mattress room on a per hour basis. The room has a small computer terminal, and mattress where you can sleep for substantially less than any hotel or hostel. In addition these places are open 24 hours per day and always have free coffee and fountain drinks. Sapporo's jiqoo is directly across from JR central station.
Nomadwiki & Trashwiki
Check Nomadwiki for info on accommodation, showers etc. or Trashwiki for dumpsters...and share your wisdom :)