Which php variable calls for Total Items in Cart?

[lat9]

Sure, here you go (with 'hard-coded' language):

$itemsInCart = $_SESSION['cart']->count_contents();
if ($itemsInCart == 1) {
  echo "Did you know a second box will ship for free!<br />"; 
} else if ($itemsInCart == 3) {
  echo 'Did you know a fourth box will ship for free!<br />';
} else if ($itemsInCart > 4 && $itemsInCart < 12) {
  echo 'Did you know that up to 12 boxes ship at no extra charge?<br />';
}