First of all, I don't do all that wimpy stuff about using a nano or gedit or 
what-not for editing my sources.list. I mean, that sounds responsible and 
orderly (and good boy scouts always follow the rules), but in the long run 
there are quicker ways. 

I gradually figure out what works, so my progress is slow but incremental at 
first; but after a few reinstallations, I get everything running as I want. 
So instead of discarding what I ought to have learned by trial and error, I 
save myself a lot of trouble in the long run by following these methods. 

I backup my sources.list like so: 
sudo 
cp -r -v -f /etc/apt/sources.list  -t /media/<WHEREVER>/sources/jessie/sources.list-orig
and change permissions so that I can edit my sources.list without being root. 
Then I open up sources.list-orig with whatever text editor (I prefer leafpad), 
making sure to save it as sources.list and not sources.list-orig. When I'm 
done, I copy it back to where it belongs like so: 
sudo cp -r -v -f /media/<WHEREVER>/sources/jessie/sources.list -t /etc/apt/
and run sudo apt-get update. 

After I have downloaded and installed pkgs, I take the precaution of saving 
them all to an external drive somewhere, and sort everything into folders (so 
that everything tde-trinity has its own folder):
sudo 
mv -v -f /var/cache/apt/archives/*.deb -t /media/<WHEREVER>/debian/jessie/tde-trinity/
and then I change permissions: 
sudo chmod -R 700 /media/<WHEREVER>/debian/jessie/tde-trinity/ | sudo chown -R 
<MYSELF> /media/<WHEREVER>/debian/jessie/tde-trinity/ | sudo chgrp -R 
<MYSELF> /media/<WHEREVER>/debian/jessie/tde-trinity/
(changing <WHEREVER> and <MYSELF>, of course, to whatever is appropriate for 
your situation. 

Then when I need to reinstall stuff, I have already sorted out what works for 
my system, so I just do: 
sudo dpkg -i -E -G /media/<WHEREVER>/debian/jessie/tde-trinity/*.deb
and install everything Trinity and TDE in a couple minutes, rather than 
waiting literally days for stuff to download. And then I run 
sudo apt-get -f install to correct any missing dependencies. 
For me, this is much faster and more reliable. Every so often I run 
sudo apt-get dist-upgrade
and then also move these packages into my folder on a separate drive. 

To reinstall my entire system as it is, by downloading packages from the 
repositories, would take at least a week. If I always waited for packages to 
download, this would be about the year 2060. Once I have figured out what 
works, I don't keep trying again and again to solve the same problems. I did 
try using aptoncd to create discs, but it seems that I need much more space 
in my root partition to use for temporary files; it worked nicely on older 
systems. And anyway, sooner or later I will upgrade to something else like 
Stretch, or switch to Devuan, or both, and then I won't need my old packages, 
so all I need to do is delete that folder, and change my commands to point to 
the appropriate places. 

I would be curious to know what are other people's methods. I've heard about 
some net installations already. 

Bill