A very useful (Windows) utility I use is TenClips - http://www.paludour.net/TenClips.html
It allows you to create enumerated clipboards/emacs-like buffers easily using
f3, etc., copy to the clipboard in the first buffer, switch to the second buffer, copy without loosing our first buffer, switch back to the first buffer and paste, switch to the second buffer and paste and so forth.
Does something like this exist for Ubuntu? The closest post I could find was Looking for an application that saves clipboard history which recommended Parcellite (http://parcellite.sourceforge.net/?page_id=2) - which keeps the history - but this is not quite what I'm after. If not I might make this a pet project :D