For all packages installed on your system:
Code:
dpkg --get-selections > file
then, to restore from this list,
Code:
dpkg --set-selections < file
apt-get dselect-upgrade
For stuff like fstab, and other files in /etc, you can build a list, and pass that to tar - or, just use tar to back up the whole directory structure under /etc, then restore it to a temporary directory and copy the files you are interested in (if not all).
Application settings, will unfortunately likely be all over the place in your home directory. .config is a new standard of sorts, but you'll find not every application you use has adapted to it. So, your settings may be found in places like
Code:
${HOME}/.config (directory)
${HOME}/.local (directory)
${HOME}/.<application_name> (can be a file or directory)
${HOME}/some_other_directory_or_file_the_developer(s)_chose (can be a file or directory)
If you expect compromised configuration files, I'd manually inspect files before backing up, or restoring.