It's The End of the World and I'm in My Bathing Suit by Justin A. Reynolds
Twelve-year-old Eddie Gordon Holloway has concocted his most genius plan ever to avoid chores . . . especially the dreaded L-A-U-N-D-R-Y. If he can wears every item of clothing in his wardrobe, summer will be halfway over before he has to do laundry!
On the day of the highly anticipated Beach Bash, Eddie ends up grounded until he can get his clothes clean. While left home alone to do his laundry, the power goes out mid-cycle. With his first load of laundry soaking wet and the rest still filthy, Eddie sets out to explore the seemingly empty neighborhood in just his swim trunks and flip-flops.
As he meets up with other neighborhood kids to find out what happened, they realize that their families aren't coming back anytime soon. And as night falls, the crew realizes they aren't just the only people left in the neighborhood -- they might be the only people left . . . anywhere.