The Gone series by Michael Grant is one of my favourite book series. It's about a beach town in California where everyone over the age of 15 disappears, and a sphere of energy covers the town so no one can get in or out. Some of the kids start developing powers, and things get out of hand. Obviously none of the above is realistic but I find it realistic in how it portrays what would happen, there's kids who are playing for power, there's the problem of food running out, kids drinking, smoking, taking drugs, sex, pregnancy, plenty of gruesome deaths, mental health issues, etc. The books have a glowing endorsement from Stephen King on the back, so that's always something.