To export the files of a container, use the command "docker container export".

Let's create a container and export its contents:

$ docker container export $(docker container create hello-world) | tar -tv

-rwxr-xr-x 0/0       0 .dockerenv
drwxr-xr-x 0/0       0 dev/
-rwxr-xr-x 0/0       0 dev/console
drwxr-xr-x 0/0       0 dev/pts/
drwxr-xr-x 0/0       0 dev/shm/
drwxr-xr-x 0/0       0 etc/
-rwxr-xr-x 0/0       0 etc/hostname
-rwxr-xr-x 0/0       0 etc/hosts
lrwxrwxrwx 0/0       0 etc/mtab -> /proc/mounts
-rwxr-xr-x 0/0       0 etc/resolv.conf
-rwxrwxr-x 0/0   13336 hello
drwxr-xr-x 0/0       0 proc/
drwxr-xr-x 0/0       0 sys/

If you check at the Dockerfile of the "hello-world" image, you will notice that it only copy the "hello" file which is the only non-empty file in the container:

FROM scratch
COPY hello /
CMD ["/hello"]

The other files and directories in the container are mandatory (required by the kernel). They all show zero bytes in length and Docker will automatically bind-mount them from the Docker host into the container when it's created.