I need to package multiple data items in PHP and publish them, how do I do that?

Instead of sending a string, send a structured message object as follows:

$big_array = array();
$big_array["msg"]["say"] = "hello";
$big_array["msg"]["what"] = "world";
$big_array["msg"]["contents"] = $myWords; 
$publish_success = $pubnub->publish(
    array( 'channel' => $pub_channel, 'message' => $big_array));

On the subscriber side, access the elements (say, what, contents) of $big_array as needed.