In the spirit of TIMTOWTDI, here's my solution.

For n items there are 2^n combinations. Create a binary string for each combination number. Check each digit of the binary string to determine if the corresponding item gets printed.

YuckFoo

#!/usr/bin/perl

   use strict;

   my (@list) = qw(one two three four);

   printcombo(\@list);

#-----------------------------------------------------------
sub printcombo {

   my ($list) = @_;
   my (@print, $str, $i, $j);

   my $size = @{$list};

   for ($i = 0; $i < 2**$size; $i++) {
      $str = sprintf("%*.*b", $size, $size, $i);
      @print = ();
      for ($j = 0; $j < $size; $j++) {
         if (substr($str, $j, 1)) { push (@print, $list->[$j]); }
      }
      print join(' ', @print) . "\n";
   }
}
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