ネットに接続できない状態でもDVDイメージのみでdebootstrapを実行できたので、その手順をメモとして以下に残します。
使用したDVDイメージは2018/11/12のdebian-testing-amd64-DVD-1.isoです。
実行環境は2018/12/01に最新化したdebian9.6です。
ユーザー環境下でsudo ./debinst.shで実効して下さい。
（debootstrapに必要な環境は事前準備願います）
応用として、ネットからdistやpoolディレクトリーをローカルにコピーし、ネット接続が無くてもある程度アプリを盛り込んだ環境を作る事は可能だと思います。
debinst.sh
#!/bin/bash
# *****************************************************************************
# debootstrap for testing cdrom
# *****************************************************************************
echo "*******************************************************************************"
echo "`date +"%Y/%m/%d %H:%M:%S"` : start [$0]"
echo "*******************************************************************************"
trap 'exit 1' 1 2 3 15
# =============================================================================
rm -rf ./debootstrap/media ./debootstrap/cdimg ./debootstrap/fsimg
mkdir -p ./debootstrap/media ./debootstrap/cdimg ./debootstrap/fsimg
# -----------------------------------------------------------------------------
mount -o loop ./debian-testing-amd64-DVD-1.iso ./debootstrap/media
debootstrap --no-check-gpg testing ./debootstrap/fsimg/ file:./debootstrap/media/
umount ./debootstrap/media
# =============================================================================
cat <<- _EOT_SH_ > ./debootstrap/fsimg/inst-dvd.sh
cp -p /etc/apt/sources.list /etc/apt/sources.list.orig
: > /etc/apt/sources.list
mkdir -p /media/cdrom
mount -o loop /debian-testing-amd64-DVD-1.iso /media/cdrom
apt-cdrom add -m --cdrom /media/cdrom
apt install -q -y --allow-unauthenticated \\
task-desktop task-laptop task-lxde-desktop task-print-server \\
task-ssh-server task-web-server task-japanese task-japanese-desktop \\
lvm2 apache2 curl rsync chromium bind9utils ntpdate network-manager \\
samba smbclient cifs-utils nfs-common nfs-kernel-server sudo tasksel \\
aptitude bc dpkg-repack build-essential perl libapt-pkg-perl \\
libio-pty-perl libnet-ssleay-perl
# ibus-mozc vsftpd clamav isc-dhcp-server apt-show-versions fdclone \\
# linux-headers-amd64 libelf-dev libauthen-pam-perl xorriso isolinux \\
# cloop-utils squashfs-tools open-vm-tools open-vm-tools-desktop \\
# chromium-l10n bind9 indent
umount /media/cdrom
# -----------------------------------------------------------------------------
cp -p /etc/apt/sources.list /etc/apt/sources.list.cdrom
cat <<- _EOT_ > /etc/apt/sources.list
deb http://deb.debian.org/debian testing main non-free contrib
deb-src http://deb.debian.org/debian testing main non-free contrib
deb http://security.debian.org/debian-security testing/updates main contrib non-free
deb-src http://security.debian.org/debian-security testing/updates main contrib non-free
# testing-updates, previously known as 'volatile'
deb http://deb.debian.org/debian testing-updates main contrib non-free
deb-src http://deb.debian.org/debian testing-updates main contrib non-free
_EOT_
# diff -y /etc/apt/sources.list /etc/apt/sources.list.orig
# diff -y /etc/apt/sources.list /etc/apt/sources.list.cdrom
# -----------------------------------------------------------------------------
sed -i /etc/locale.gen \\
-e 's/^[A-Za-z]/# &/g' \\
-e 's/# \\(ja_JP.UTF-8 UTF-8\\)/\\1/g' \\
-e 's/# \\(en_US.UTF-8 UTF-8\\)/\\1/g'
locale-gen
update-locale LANG=ja_JP.UTF-8
# -----------------------------------------------------------------------------
for TARGET in "/etc/skel" "/root"
do
pushd \${TARGET} > /dev/null
cat <<- _EOT_ >> .bashrc
# --- 日本語文字化け対策 ---
case "\\\${TERM}" in
"linux" ) export LANG=C;;
* ) ;;
esac
# export GTK_IM_MODULE=ibus
# export XMODIFIERS=@im=ibus
# export QT_IM_MODULE=ibus
_EOT_
cat <<- _EOT_ > .vimrc
set number " Print the line number in front of each line.
set tabstop=4 " Number of spaces that a <Tab> in the file counts for.
set list " List mode: Show tabs as CTRL-I is displayed, display $ after end of line.
set listchars=tab:\>_ " Strings to use in 'list' mode and for the |:list| command.
set nowrap " This option changes how text is displayed.
set showmode " If in Insert, Replace or Visual mode put a message on the last line.
set laststatus=2 " The value of this option influences when the last window will have a status line always.
_EOT_
cat <<- _EOT_ > .curlrc
location
progress-bar
remote-time
show-error
_EOT_
popd > /dev/null
done
# -----------------------------------------------------------------------------
apt -q -y autoremove
apt -q autoclean
apt -q clean
_EOT_SH_
# =============================================================================
cp -p ./debian-testing-amd64-DVD-1.iso ./debootstrap/fsimg/
# -----------------------------------------------------------------------------
mount --bind /dev ./debootstrap/fsimg/dev && mount --bind /dev/pts ./debootstrap/fsimg/dev/pts && mount --bind /proc ./debootstrap/fsimg/proc
LANG=C chroot ./debootstrap/fsimg/ /bin/bash /inst-dvd.sh
umount -lf ./debootstrap/fsimg/proc && umount -lf ./debootstrap/fsimg/dev/pts && umount -lf ./debootstrap/fsimg/dev
# -----------------------------------------------------------------------------
find ./debootstrap/fsimg/var/log/ -type f -name \* -exec cp -f /dev/null {} \;
rm -rf ./debootstrap/fsimg/debian-testing-amd64-DVD-1.iso \
./debootstrap/fsimg/inst-dvd.sh \
./debootstrap/fsimg/root/.bash_history \
./debootstrap/fsimg/root/.viminfo \
./debootstrap/fsimg/tmp/* \
./debootstrap/fsimg/var/cache/apt/*.bin \
./debootstrap/fsimg/var/cache/apt/archives/*.deb
# =============================================================================
echo "*******************************************************************************"
echo "`date +"%Y/%m/%d %H:%M:%S"` : end [$0]"
echo "*******************************************************************************"
exit 0
# == memo =====================================================================
# sudo bash -c 'mount --bind /dev ./debootstrap/fsimg/dev && mount --bind /dev/pts ./debootstrap/fsimg/dev/pts && mount --bind /proc ./debootstrap/fsimg/proc'
# sudo bash -c 'LANG=C chroot ./debootstrap/fsimg/'
# sudo bash -c 'umount -lf ./debootstrap/fsimg/proc && umount -lf ./debootstrap/fsimg/dev/pts && umount -lf ./debootstrap/fsimg/dev'
# -----------------------------------------------------------------------------
# tar -cz ./debootstrap/fsimg/inst-dvd.sh | xxd -ps
# cat <<- _EOT_ | xxd -r -p | tar -xz
# -----------------------------------------------------------------------------
# sudo apt -y install squashfs-tools xorriso cloop-utils isolinux
# == EOF ======================================================================