<script>
$('product_li a).click(function(){
    $.cookie("li_click_data", $(this).parent().innerhtml());
    return true;
});
</script>
......
<li class="product_li"><a href="xxx">your product title</a></li>

$_COOKIE['li_click_data'];

// for list_items.php
foreach($item as $i) {
    // Do what you normally do, but also set an array in the session.
    // Presuming you have an id or some other means (here as item_id), to identify
    // an item, then you can also access this array on the item_details -page.
    $_SESSION['mystic_item_data_array'][$i['item_id]] = $i['thedata'];
}

// For item_details.php
$item_id = // whatever means you use to identify items, get that id.
$data_you_need = $_SESSION['mystic_item_data_array'][$item_id];