[Monkeyhead]

Got it!

Find the file include/func/func.cart.php

In the file find the code:

 #
		# Set the fields filter to avoid storing too much redundant data
		# in the session
		#
		list($tmp_k, $tmp_v) = each($cart["products"]);

		foreach(array_keys($tmp_v) as $k)
			$product_keys[] = $k;

		unset($tmp_k, $tmp_v);
		reset($cart["products"]);

		$product_keys[] = "cartid";
		$product_keys[] = "product";
		$product_keys[] = "productcode";
		$product_keys[] = "product_options";

[/php]

Add this line to the product keys

$product_keys[] = "descr";

Then in customer/main/cart_details.tpl you can add the {$products[prod_num].descr|truncate:"30":"...":true} where required.