There are three different public transport in Dublin. Bus, DART (Dublin Area Rapid Transport), and LUAS a new tramway with two lines.
The buses in Dublin have two floors, like in London. There are a lot of lines, and they are really useful. Usually they are running from 6:00 to 23:00. There are two different way for paying the bus. You can pay directly the bus driver, you have to pay for the ride from 1,4€ to 2.65€, you have to pay with coins, and you can't get the change. There is also a ticket for very short ride in city center for 0.6€. The second way to pay is to buy day ticket, you can get it in a lot of shops and kiosks in the city. One day ticket is 6,9€, one day family ticket is 11,9€ (2 alduts, 4 children), one five days ticket is 23€, and one 3 days ticket is 14,2€. It is easy to go in the bus without paying. The machine where you have to check with your day ticket is not in the front of the driver. What you can do is just get an old ticket, and do as it was a valid ticket, it sounds different and there is a red light instead of green or orange, but usually nobody notice. You can also try to pass without checking any ticket, it also work. It seems that the worst that can happen to you is the driver kick you off the bus. Website : http://www.dublinbus.ie/.
The DART only have one coast line. From Greystone to Malahide. It is a nice journey. For example the journey from Connolly to Malahide is 2,5€. And there are also tickets for one, three, and five days. Website : http://www.dublin.ie/transport/dart.htm
In Ireland, almost everything is more expensive in the supermarket than in continental Europe. But you can get a good meal in a snack or a pub starting at 5€.
Dumbster diving is known to be easy. And getting vegetables and fruit at the end of the market is easy too.
You can find free wifi spots in a lot of shops or bars in the city center. There is also free wifi on some buses.
There are bylaws that regulate busking. Buskers are supposed to buy annual permits costing €30, or €60 for an amplifier, to perform on the streets, and a two hour time limits on performances. Buskers are allowed to use amplifiers, but must restrict their noise levels to 80 decibels, and 75 decibels in Temple Bar.
They also limit times for busking to between 9am and 11pm (with exceptions for Grafton Street). Buskers will not be able to stand within fifty feet of another entertainer. For more information, you can read the bylaws here.
Many of Dublin's freegans hang out in Seomra Spraoi, an autonomous social centre near Mountjoy Square in the city centre. If you come to Seomra on a Wednesday evening (food is served at 7:30), there's a vegan café there and you should be able to meet them and hopefully arrange to go skipping with them sometime. You may also be interested in the bike workshop at Seomra, which is also open on Wednesday evenings. It is well equipped with tools and expertise and it's a great way to learn how to look after your own bike. In particular, it's handy for fixing up any abandoned bicycles you might happen to come across. Seomra also has a decently-sized freeshop upstairs, which is open whenever Seomra is open. It is particularly good for clothes. The website says that it's usually open from Monday to Thursday from 6 to 10pm. http://seomraspraoi.org/