ขอคำปรึกษาเรื่อง ทำ shopping Cart และระบบ แลกของแถมหน่อยครับ

if(array_key_exists($pid, $_SESSION['cart_items'])){
 $_SESSION['cart_items'][$pid]['qty']+=$qty;
}else{
 $_SESSION['cart_items'][$pid]['product_id']=$pid;
 $_SESSION['cart_items'][$pid]['product_name']=$name;
 $_SESSION['cart_items'][$pid]['qty']=$qty;
$_SESSION['cart_items'][$pid]['status']='$status'; // สถานะของแถม
}

    [cart_items] => Array
        (
            [00001] => Array
                (
                    [product_id] => 00001
                    [product_name] => A
                    [qty] => 1
                )
            [00002] => Array
                (
                    [product_id] => 00002
                    [product_name] => B
                    [qty] => 9
                )
)