#To replicate your packages selection on another machine (or restore it if 
#re-installing), you can type : 
dpkg --get-selections > ~/my-packages 
#move the file "my-packages" to the other machine, and there type : 
sudo dpkg --set-selections < my-packages && sudo apt-get dselect-upgrade

#Or you could just use Remastersys. Which is 20million times more amazing.
#http://www.remastersys.klikit.org/