# Create the cart
my $cart = new Cart( type => 'DBI', id => $foo ); 
print "Cart's current total is: ", $cart->total_cost();

# Be sure we don't sell anything inappropriate!
foreach my $item ( $cart->list_items ) {
    if ( $item->type eq 'adult' && $user->age < 18 ) {
        $cart->remove_item( $item );
    }
}
$cart->save;
print "Cart's new total is: ", $cart->total_cost();