In the live system on the Simply Linux 6.0.2 DVD, APT is not configured to take the packages from the DVD.

It would be convenient if it were, because there are more packages on the DVD than there are installed in the live system.

The configuration of APT could either list the package repository on the DVD (mounted at /image/) as a repo to be accessed as files, or as a cdrom...

For example, I tried to give the correct options to APT to manually access it as a CD, they turned out to be something like:

apt-cdrom --cdrom /image/ --no-mount add

apt-get update
apt-get -o cdrom::Mount=/image/ -o cdrom::/image/::Mount=/bin/true cdrom::/image/::UMount=/bin/true install 

Also, an option that says APT not to copy the packages acquired from the CD into the cache would be good -- in order to occupy less of the valuable RAM.

Probably, configuring this source as a file source would be simpler.