Where do you camp (or stay) when all of the campsites are booked?

I do plan on reserving the sites I can get at the available campsites but was just wondering.

Backcountry campsites is an option but limited in quantity plus you need an off-road vehicle.

It's not like there's motels/hotels near by.

You can't camp just anywhere.

There's 800k acres of park but not too many places to camp.

Where do people stay when everything is full?