my %items = ( z => [ qw/one six/ ],
              'y' => [ qw/two three five/ ],
              x => [ qw/one two five/ ],
            );

my %corr;

foreach my $item (keys %items) {
   my $max = scalar @{$items{$item}} - 1;
   for my $first (0..$max) {
      for my $second ($first+1..$max) {
         $corr{ $items{$item}[$first] }{ $items{$item}[$second] }++;
      }
   }
}

for my $first (keys %corr) {
   for my $second (keys %{$corr{$first}}) {
      print "$first $second: $corr{$first}{$second}\n";
   }
}