S-bahn and U-bahn have no access barrier as in most german cities; i.e. extremely easily blackrideable, just be careful of checkers as usual but not a big deal, less frequent than Berlin.
Black riding is possible, albeit risky. Controllers are very frequent and often wear civil clothes, so they cannot be noticed before the doors are closed. And since they do not receive an hourly wage but a salary depending on how many people they catch, playing the "dumb tourist" will have no effect on them; they want you in their record. It is very easy to fool them however, they will first ask you for a national ID or a passport and if you tell them that you cannot produce either they will accept anything that has a (supposedly your) name and an address on it. They can't be bothered to call the police as that takes them a lot of time to arrive. Anything from a fake organ donor card, a bank account statement or a letter addressed to you will do - even if that's hand written. For routes of public transport check hvv.de or http://www.geofox.de/base/welcome.jsp
- FB group for info about black riding in Hamburg
Accommodation & Wild Camping
As far as Fede visited the city (november 2013) the Hamburg Occupy movement was still camping and occupying the streets in Gertrudekirchhof, very close to the central station (where by the way being careful and nice you can ask lots of homeless or punks for a nice spot to sleep); wheter you have a tent or not if just for a couple of nights they welcome you and find a place to sleep. If not asking in Alimaus and Kafe mit Herz you should find some public dormitories.
The religious associations "Alimaus" (Nobistor 42, S-bahn "Hamburg Reeperbahn" check also (in german) http://www.alimaus.de/docs/153034/kontakt.aspx) and "Cafe mit Herz" (Seewartenstr. 10, U-bahn St.Pauli http://www.cafeemitherz.de/redesign/) provide free breakfast and lunch (different timetables but approximately breakfast till 11.30 a.m and lunch from 3 p.m); more than free clothes (be there early in the morning) showers and laundry. They have also connections to find free german classes and cheap flats
Free drink refills, pick up a cup and get high on fizzy drinks at:
Mundsburg(U3) in McDonalds
Billwerder-Moorfleet(S21) in IKEA
With free IKEA card you can drink unlimited free coffe
Cheap internet cafes are available for 1€/h 10 min away from central station. Wifi is free in several places
At Hauptbahnhof in McDonalds.
Inside Mercado near Altona Station (between the Reformhaus Englehart and the escalator)
Zentralbibliothek (Central Library) near Hauptbahnhof
In front of the Apple store, Jungfernstieg
As of April 2016, in "Am Borgweg" and "Mönckebergstraße" U-bahn stations
Spitalestrasse is a very good and contended place for buskers. All the way down from the central station till Mönckenbergstrasse is really full of people from the afternoon onwards and provide very good money finding a nice spot. Even though is probably necesary a permit as anywhere else in this world, police most probably won´t tell you anything and especially if for a couple of days you will have to deal only with the otehr buskers