use Math::Combinatorics;

my $nwordsatonce = 4;
my ($k,$v);
my %totals = ();
local $" = ' ';  # just in case
while (($k,$v) = each %items)
{
  next unless $nwordsatonce <= @$v;
  my @words = sort @$v;
  do {$totals{"@$_"} += 1;} for combine($nwordsatonce,@words);
}

my @comb = sort {$totals{$b} <=> $totals{$a}} keys %totals;
print "Top $nwordsatonce - word combinations:\n";
do {print "$_\n";} for @comb[0..4];