I'm not quite clear on what you're attempting to combine here.
Are you trying to combine a bunch of Perl code into a central collection which can be accessed by multiple CGI programs? If so, look for information on creating Perl modules.
Are you trying to build individual pages by assembling reusable pieces of HTML, such as standard/shared headers, footers, or sidebars? If so, you need a templating system. Template::Toolkit is the current 800-lb gorilla of Perl templates, but there are other good options out there, such as Alloy (which is mostly TT-compatible, but faster) and Xslate (my current preference).