Today I found myself thinking about the best documents in the perldoc collection. I end up thinking that one could learn learn almost all you need of Perl simply by reading perlintro (the basic introduction), perlreftut (the tutorial on references and how to use them) and perltoot (Tom's Object-Oriented Tutorial).
The last could be omitted if you wanted to use Moose OO, however reading it still gives insight into how a hashref-based object works. Moose objects are still constructed in this way even if you don't see it.
Of course there is far more to learn from perldoc and once you include the documentation from modules this pool of knowledge is endless. I know documenting your modules is a pain, but good documentation is one of Perl's great strengths!