I often miss Java's standard object methods toString, equals, compareTo, perhaps serialise.
The first three would usually be done with overloading, I guess, and serialization depends on the format (like Storable or one of the many text-based formats). I wrote a bit about the complexity of equals and hashCode in this node.
Another thought is to provide a *safe and proper* way to convert from a string representation of a perl data structure(pds) to pds
I tried to do something like that with Config::Perl (see Undumping Perl).