Me and a friend are thinking about bring our guitars into the city and just jamming, hopefully getting some donations to make a few bucks. I was wondering if it is legal to play on the sidewalks/ subway station? And if so, what are some good songs to play on the streets?
In the U.S. and many other countries, you're free to set up and play on public property as long as you're not obstructing passers-by or otherwise creating a nuisance. Typically the worst that can happen is that someone will ask you to leave.
Police and store owners are almost always very nice about asking you to leave, and you should be nice, too..
In the United States under Constitutional Law and most European common law, the protection of artistic free speech extends to busking. So give it a try!