title: Modify preseed file to automatically install packages in /pool/extra
body: <p>I want to modify the preseed file of an unpacked (using UCK) GNU/Linux ISO, and then re pack it (using UCK).</p>
  
  <p>What I am trying to do is, modify the preseed file in such a manner that what all packages in .deb format I copy to the <code>pool/extras</code> folder, they get installed automatically during the OS installation. 
  For that I will need to add something in the preseed file. I have not been able to figure out what it is. Can someone please help me out?</p>