See (and mark) ticket inspectors on the map when they've spotted: http://www.smurff.it/
It is partially possible to blackride Helsinki public transport. Trams and metro can be entered without turnikets/drivers checking. In trams controls are not so frequent. You can sit in the front and look at stops if controllers are there. They can wear blue uniforms or be in civil clothes; probably in two or groups (didn't meet them).
Beware in metro, controllers can wait under escalators.
Trains named by letters (S, U, L, E, P, ...) can be black-ridden successfully. People in green striped T-shirts and gray vests are just selling tickets, not checking. Control can be random in similar fashion to metro or tram.
Buses are not blackrideable. Drivers are checking your card or selling tickets except for 560 and 550 but controls can still happen (rarely).
Price for single ticket (80 minutes) is 3 EUR for zones A-B (basically inside Helsinki and partly Espoo). It can be bought from drivers. Global fine for blackriding is 80 EUR. What happens if you get caught and (don't have money) or (refuse to pay) and (don't prove your identity) needs to be researched.
Accommodation & Wild Camping
There are many green areas around Helsinki where it may be possible to camp. Be cautious of Kaisaniemen puisto for overnight stay thought.
Keskuspuisto (Central Park) is a large forest area near the centre.
Mustikkamaa island can be an option for a short term camping. Stay away from the guarded beach. It can get quite crowded in the morning, especially in sunny summer days. There are cold outdoor showers at the guarded beach and a water source behind the wooden buildings. Note that there is a new walk + cycle bridge to the island, which is not marked on paper touristic maps. Please use this camping option only for a day or two and don't make fire and mess. The places are quite exposed and overuse/misuse may start bothering people. Also stay away from buildings.
There are forests and lakes further from Helsinki which could be used even for longer camping. Some places have fireplaces, wood or a simple shelter. For example Uutela forest 15km from Helsinki center in far eastern part of the city.
Shower & swiming
Add info pls
Check trashwiki. Many good dumpsterdiving places around the city center were closed because people were leaving mess around. Dumpster-diving can still be very nice outside of the center. Please keep the places tidy.
City has free wifi network called "Helsinki City Open WLAN". See map.
Helsinki-Vantaa airport has a free wifi. Metro stations as well.
Libraries are a great option for sitting and working on the internet. Some are open even on Sundays. A library next to the central train station has a 3D printer, sewing machines and more.
Busking is allowed. Police doesn't make problems. There are many musicians performing around the center, so competition in music can be hard.
Free work place
You can go to Microsoft's "Flux" office to work for free. They have desks, coffee, printers and 3D printers. Korkeavuorenkatu 35, 2nd floor. More info
Sompasauna is a free public sauna near Helsinki centre. It's always open and often there are people. It's a good idea to take a towel to sit on for hygienic reasons: many different people come there. Read more from sompasauna.fi or check the video
Free bike repair place organized by city is in front of Kamppi shopping centre every weekday till 6 pm.
An anarchist bike workshop is open every Sunday and Wednesday from 4 pm.