To show the custom attribute label and value in a magento cart we do the following

suppose attribute_code is myvar

it's ID/VALUE is 7 and LABEL = Myvar

create config.xml of module with the following code

<global>
    <sales>
        <quote>
        <item>
            <product_attributes>
            <section/>
            </product_attributes>
        </item>
        </quote>
    </sales>

And in cart.phtml

$_item->getProduct()->getSection();

This code will return ID/VALUE of attribute 7

by using this value we will get the label as

$_product = Mage::getModel('catalog/product');
$attr = $_product->getResource()->getAttribute("myvar");
if ($attr->usesSource()) {
    $_label = $attr->getSource()->getOptionText("7");
}