Can someone help me with nanowrimo teen fantasy fiction?

Okay so i love teen fantasy fiction books like lord of the rings, percy jackson, harry potter, chronicles of narnia, his dark materials and stuff and I want to make my story for nanowrimo in that genre but it's hard to come up with something that hasn't already been done because i dont want to write about wizards or anyone with magical powers or anything but i dont wnat to make them just humans because that would be boring. and i want them to go on some sort of quest that comes down to saving or destroying the world but its all been done before so what should i do