a couple of things,

The major problem with the code you have there is that it doesn't give combinations of separated list items, it only gives items from one point forward. As an example:
for n=3, with items 1,2, and 3, i get the following from your code:
1
1 2
1 2 3
2
2 3
3
Note the missing '1 3' case. For the items 1,2,3, and 4, '134', '124', '13', '14', etc would be missing.

Merlyn's snippets are a nice and easy way to go; a simple transformation and they will return an array of strings instead of an AoA. As an exercise, i chalked up a non-recursive solution as well; it returns an array of arrays as merlyn's does.

sub combinations {
  my (@comb, $pos);
  my $limit = 2**@_;

  while (my $item = shift) {
    my $step = 2**@_;
    for ($pos = 0; $pos < $limit; $pos += $step) {
      push @{$comb[$pos++]}, $item for 1..$step;
    }
  }

  return @comb, [];
}
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jynx