<?xml version="1.0"?> <config>
    <modules>
        <MyCommentBox_CommentBox>
            <active>true</active>
            <codePool>local</codePool>
            <depends>
                <Mage_Checkout/>
            </depends>
        </MyCommentBox_CommentBox>
    </modules> </config>

<?xml version="1.0" encoding="UTF-8"?><config>
     <modules>
         <MyExtensions_CommentBox>
             <version>0.1.0</version>
         </MyExtensions_CommentBox>
     </modules>

     <frontend>
         <routers>
             <checkout>
                 <args>
                     <modules>
                         <MyExtensions_CommentBox before="Mage_Checkout">MyExtensions_CommentBox</MyExtensions_CommentBox
                     </modules>
                 </args>
             </checkout>
         </routers>
     </frontend>
 </config>

require_once 'Mage/Checkout/controllers/CartController.php';
    class MyCommentBox_CommentBox_CartController extends Mage_Checkout_CartController {

    public function addAction()
     {
        if (!$this->_validateFormKey()) {
             $this->_goBack();
             return;
        }
        $cart   = $this->_getCart();
        $params = $this->getRequest()->getParams();
        try {
            if (isset($params['qty'])) {
                $filter = new Zend_Filter_LocalizedToNormalized(
                    array('locale' => Mage::app()->getLocale()->getLocaleCode())
                );
                $params['qty'] = $filter->filter($params['qty']);
            }

            $product = $this->_initProduct();
            $related = $this->getRequest()->getParam('related_product');

            /**
             * Check product availability
             */
            if (!$product) {
                $this->_goBack();
                return;
            }
            /****************/
            /* Custom Params*/
            /****************/
            //Create custom option
            $additionalOptions = array(array(
               'code' => 'my_code',
               'label' => 'This text is displayed through additional options',
               'value' =>  $this->getRequest()->getParam('textOpt');
            ));
            //Add Custom Option to product
            $product->addOption($item->addOption(array(
                'code' => 'additional_options',
                 'value' => serialize($additionalOptions),
            ));
            /****************/
            $cart->addProduct($product, $params);
            if (!empty($related)) {
                $cart->addProductsByIds(explode(',', $related));
            }

            $cart->save();

            $this->_getSession()->setCartWasUpdated(true);

            /**
             * @todo remove wishlist observer processAddToCart
             */
            Mage::dispatchEvent('checkout_cart_add_product_complete',
                array('product' => $product, 'request' => $this->getRequest(), 'response' => $this->getResponse())
            );

            if (!$this->_getSession()->getNoCartRedirect(true)) {
                if (!$cart->getQuote()->getHasError()) {
                    $message = $this->__('%s was added to your shopping cart.', Mage::helper('core')->escapeHtml($product->getName()));
                    $this->_getSession()->addSuccess($message);
                }
                $this->_goBack();
            }
        } catch (Mage_Core_Exception $e) {
            if ($this->_getSession()->getUseNotice(true)) {
                $this->_getSession()->addNotice(Mage::helper('core')->escapeHtml($e->getMessage()));
            } else {
                $messages = array_unique(explode("n", $e->getMessage()));
                foreach ($messages as $message) {
                    $this->_getSession()->addError(Mage::helper('core')->escapeHtml($message));
                }
            }

            $url = $this->_getSession()->getRedirectUrl(true);
            if ($url) {
                $this->getResponse()->setRedirect($url);
            } else {
                $this->_redirectReferer(Mage::helper('checkout/cart')->getCartUrl());
            }
        } catch (Exception $e) {
            $this->_getSession()->addException($e, $this->__('Cannot add the item to shopping cart.'));
            Mage::logException($e);
            $this->_goBack();
        }
     }

    }

/****************/
            /* Custom Params*/
            /****************/
            //Create custom option
            $additionalOptions = array(array(
               'code' => 'my_code',
               'label' => 'This text is displayed through additional options',
               'value' =>  $this->getRequest()->getParam('textOpt');
            ));
            //Add Custom Option to product
            $product->addOption($item->addOption(array(
                'code' => 'additional_options',
                 'value' => serialize($additionalOptions),
            ));
            /****************/