I?ve been working with 15/16 year olds and tend to focus on a comparison between their own lives and experiences and those of British teenagers - I get the info from the teenage kids of friends in Britain. I e-mail them with questions like -
How much money do you have to spend each week? Where do you get it? What do you spend it on? etc, then ask my students the same questions. After they've discussed it I give them the reply E-mail to read, to compare (sometimes a "cleaned up" version, I admit). It brings out differences like the fact that older British teens often have evening or Saturday jobs - which in Italy is unheard of, and so on. Other topics I've used have been school subjects, school regulations, gap year plans, and the Duke of Edinburgh award system.
Another good source of info, especially for younger teens, is the
CBBC site. I've linked for example to a section where they asked the kids to tell them their experiences on school trips - another topic you could use contrastively. I also once used a good one from the same site written by a 14 year old who was a keen actor and about to audition for the National Youth Theatre. Can't find the link unfortunately but it will give you some idea of the stuff that's on the site.
Being in Italy a lot of the kids go to Britain for summer courses, so I also do some work to prepare them for the cultural differences they're going to come up against when they stay with host families etc. You can find the quiz I use
here.