If you administrates an offline Trisquel, bring on it (e.g., using a USB
stick) the .deb package of 'apt-offline' and install it with GDebi or 'sudo
dpkg -i':
http://archive.trisquel.info/trisquel/pool/main/a/apt-offline/apt-offline_1.1.1build1_all.deb
for Trisquel 6;
http://archive.trisquel.info/trisquel/pool/main/a/apt-offline/apt-offline_1.3.1ubuntu0.1_all.deb
for Trisquel 7;
http://archive.trisquel.info/trisquel/pool/main/a/apt-offline/apt-offline_1.7_all.deb
for Trisquel 8.
Its dependencies ("apt", "less" and "python") are already installed: even
"trisquel-minimal", which provide a minimal console environment, depends on
them. Then use the 'apt-offline' command to manage all your packages. If
you like GUIs, the first package you want to install with that command is
"apt-offline-gui". You can then use its GUI.