mitfahrgelegenheit.de and mitfahrzentrale.de are popular commercial websites for carpooling. However, since they started charging a certain percentage for each ride they mediate, there are new pages starting to be used more and more. Some of them are: bessermitfahren.de; blablacar.de.
Germany is one of the easiest countries for hitchhiking.
Bahn.de is quite expensive. Sometimes it makes a lot of sense to get a 25% reduction Bahncard simultaneously while buying a ticket as you can earn back the cost of the card with just 1 ticket already. Just make sure you cancel the Bahncard right after you get it, otherwise your stuck to a yearly subscription.
You can try to "hitch" group tickets in the weekend, as more people are traveling with tickets that allow up to 5 people to travel with just one ticket. However, this has gotten more difficult recently, as the Deutsche Bahn started to require everyone's name written down on the ticket. They might check for IDs to see if you're actually the person whose name is on the ticket but they barely do it.
Ltur often has good "last minute" deals that, from 26 euro within Germany (book between 1 and 7 days ahead) and 36 euro abroad (book between 3 and 14 days ahead).
In general, it is quite easy to take trains without a ticket but the legal consequences are worse than in most countries if you get caught. "Obtaining services under false pretenses" is a criminal offense with a one year prison sentence as a maximum penalty. Depending on the tricks you use, you might also be charged with fraud. However, you will usually just be issued a fine by the train company (60€ or the double amount of the ticket price, depending on which is more) and if you pay it and you don't get caught more than three times, you probably won't be criminally charged at all. Ask local people for good tricks, there are proper ways of taking pretty much every train without a ticket.
There are some relatively new low budget bus options available:
busradar.com is a great website for comparing prices of long-distance buses, trains and ride shares.
one important keyword for alternative life in Germany and in general in German speaking countries is "Wagenplatz" (also called "Wagenburg" or "Wagendorf"), which is sort of a little village out of wagons, vans or other wicked vehicles where people live. Every Wagenplatz is different and there are some more secluded than others, but they are usually keen on helping like-minded travelers. Also some of them in the cities use to hold "Volksküche" in the summer as well as many other events. They use to be very engaged with the alternative scene. You can find a list of them here (although not complete and unfortunately in German): http://www.wagendorf.de/index.php/Links#Wagenpl.C3.A4tze
Wild camping is generally prohibited in Germany, but is barely monitored. If you don't raise too much attention, you will be fine.
In many german cities you can find so called "Voküs" which is short for "Volxküche" (peoples kitchen). There you can eat for free or donation. Ask for Voküs in Squats, social centers or other alternative places. Here you find a list of vegan Voküs: http://de.veganwiki.org/vegane_vokue
Also dumpster diving works pretty well all over Germany, but watch out for cops, while you do it, they might cause you problems. Try to get to the supermarkets when they already have been closed for at least an hour. Otherwise, it's quite likely to be spotted by workers. They will usually just chase you away if they see you for the first time but they also might call the cops. Dumpster diving is considered theft in Germany. For many dumster diving spots, you'll have to climb over a gate or a fence so you can be charged with trespassing as well. If the dumpster is accessible without any barriers, it's not considered trespassing (unless you don't leave the property if a worker tells you to do so).
Blau.de is a good deal. Aldi could be cheaper but has fewer options to add credit.
If you are looking for events, concerts, and parties in Germany, those websites could help you :
Busking generally works great in Germany, especially in medium-sized towns. People tend to appreciate what you are doing and if you busk with a group, it's quite common to have a crowd gathering around you. Laws differ from town to town and are quite different. In many places, busking is legal but restricted in terms of duration, spots, time of the day etc. In some places, you will need a permission. Usually, you will be fine no matter if you pay attention to the laws or not. You might be sent away by "Ordnungsamt"-officers (something like police for minor offenses). Sometimes, you will get a fine. If you don't care about what they told you and continue playing music, they might seize your instruments or call the cops.
Germany is part of the Schengen area.