Another "horrible-alternate-world-scenario" suggestion from Julie the teen librarian, How I Live Now isn't a high tech horror story like Feed. It's scarier because it's far more realistic. The 15-year-old protagonist, a New Yorker with n eating disorder and a wicked stepmother finds herself vacationing with her cousins (one of the kissing variety) in England when war breaks out. Their house gets "sequestered," and children get separated by gender. The rest of the story is of their survival and how they find one another again.
I think my favorite character (See, it really is about character for me.) is 9-year-old Piper, a dog whisperer who though kind of psychic, isn't as good at telling good mushrooms from bad as she would like. The book's ending isn't its strong point, but I still liked it for its down to earth depiction of kids on their own in a world that ranges from indifferent to hostile.
Staying alive is what we did to pass the time. p.155