PHP Function to find the last key of a multidimensional array

This function is great for retrieving the last key of a multidimensional array. I use this function on a site that stores cake options such as size, shape, ribbon colour, icing colour and text fields for use in a shopping basket. Not all cakes have all the options so i need to know where the end of the array is, hence this function.

Hope this helps people, if there is a better way of doing it, please feel free to discuss in the comments.

array_push($_SESSION["cake"]["items"], array(
    "product" => $_POST["id"],
    "size" => $_POST["cake-size"],
    "message" => $_POST["cake-message"],
    "style" => $_POST["shape"],
    "flavour" => $cakeflavour[0],
    "qty" => 1));

    $arkey = array_pop(array_keys($_SESSION["cake"]["items"]));