I think that certain things you can get away with and others you can't. I mean, some would say that music or movies, etc would date your work, but all the time you see books where the MC is into 'oldies'. It all comes down to how you present it.
I think if you say in the book that the MC is going to see The Ring at the theatre, yeah, you've totally dated yourself. Even by today's standards it's dated. Naming specific movies isn't a good idea...even if it isn't in the movies. Tape became DVD, DVD became Blueray and so on. It's dated. Say the genre (a horror movie), not the title, or make a title up.
For music, you could say something like your MC has his headphones in and is tuning out to some heavy metal, and get away with it. Today's generation immediately thinks 'iPod' and identifies with the generic description. When something better than the iPod comes along, they will see headphones and think of the new media. Even terms like cell phones, texting, and handhelds still will hold their value to a certain degree. However, if you said MP 3, well..you've dated yourself.
Because technology is a huge part of this generation's culture, it's unwise to avoid it if you're writing contemporary. Some of the realism will be lost. Just don't be so specific that it dates your work. Keep it relatable.
As for slang, I think if you make the slang fit the character, you'll be on the right track. Instead of saying 'for shizzle' (groan) try something that will fit. Teens often shorten or splice words together to create slang. Whatever became whatev. Think of something new. The authenticity of it will come when it fits your character's style. If your character can use it confidently, it will feel real.
I think there are some slang that handles the test of time, like: Oh God, Are you kidding me? No way (sometimes), Damn, Real nice (as a sarcastic term), etc. As I said, I think it has to 'feel' right coming from the character's mouth or through their thoughts.