Call me old-fashioned, but I almost never use the following (although sometimes I use modules that do).

• source filters
• prototypes
• formats (well, that would be old-fashioned)
• tie (although it has been a helful hack for debugging in some occasions)
• attributes (including lvalue)
• barewords (not counting those that are allowed under "use strict")
• "experimental" regex features. They look cool, but I've been bitten by their bugs too many times. I was surprised to see that Damian recomends some of them as best practices!
• AUTOLOAD
• CHECK, INIT
• CORE::GLOBAL (sometimes useful, such as for testing)
• Most of the variables on perlvar, but that's too long to mention here. Many of the functions in perlfunc as well.
• <> to glob
• foreach (heh, I'm to lazy to type those extra characters. But of course I use for!)
• pseudohashes (they have been deprecated anyway)
• version strings (also deprecated)
• until