1. Hide the "display_price" for 0-values
   /modules/uc_multi_currency/uc_multi_currency.theme.inc:18:
    if ($variables['price'] > '0.00') {
  $output = '<span class="uc-price">'. uc_multi_currency_format($variables['price'], $currency) .'</span>';
  }
  else {
  $output = '';
  }
   modules/ubercart/uc_store/uc_store.theme.inc:19:
   if ($variables['price'] > '0.00') {
  $output = '<span class="uc-price">' . uc_currency_format($variables['price']) . '</span>';
  }
  else {

<style type="text/css">
#my_cart_items {