How do I add a $( document ).ready() function to this script?

I tried reading and inserting the document function in this code but I have no idea what im doing. Can someone tell where I should put the document initialization and why? this would be of great help. thanks.

Here's a fiddle of what the jquery is for

<script type="text/javascript">
$('.quantity, .drink').change(calculateTotal);
function calculateTotal() {
    var $form = $(this).closest('form'), total = 0;
    $form.find('.drink:checked').each(function() {
        total += $(this).data('price') * parseInt($(this).next('.quantity').val() || 0, 10);
    });

    $('#totalDiv').text(total);
}
</script>