my $foo = new Foo;

$foo->add_item("Cheese");
$foo->add_item("Mice");
$foo->add_item("Rat", "Cat");

use Data::Dumper;
print Data::Dumper->Dump([$foo], ['foo']);

package Foo;

sub new {
    bless { _orderid => '', _items => [] }, $_[0];
}

sub add_item {
    push @{ $_[0]->{_items} }, @_[1 .. $#_];
}

##</code><code>##

$foo = bless( {
                '_orderid' => '',
                '_items' => [
                              'Cheese',
                              'Mice',
                              'Rat',
                              'Cat'
                            ]
              }, 'Foo' );