A group of friends went camping in the nearby forest/mountains/lake. When they get back to town, they find out that a virus had swept across the countryside and destroyed everyone and everything.
– OR –
A group of friends goes camping in the nearby forest/mountains/lake. While they’re out there, they see a meteor fall from the sky in the direction of their homes. They pack up and head back only to find that their sleepy little town has been infected/invaded and it’s up to them to stop it from spreading.