[advantageco]

Seems I have solved my own problem to a point, here's what I did:
-Added new field 'ranumber' to 'xcart_order_details' table
-Added new line in func.order.php (711)

$insert_data = array (
                    'orderid' => $orderid,
                    'productid' => $product['productid'],
                    'product' => addslashes($product['product_orig']),
                    'product_options' => addslashes($product['product_options']),
                    'amount' => $product['amount'],
                    'price' => $product['price'],
                    'provider' => addslashes($product["provider"]),
                    'extra_data' => addslashes(serialize($product["extra_data"])),
                    'productcode' => addslashes($product['productcode']),
                    'ranumber' => '$MYRANUMBER'); //This is the line I added.

Next steps for me is to add the functionality to display the RA# in the cart, invoice, and orders pages which will be a piece of cake after this.