One way around Drupal 7 Ubercart 7.x-3.5 cache anonymous cart (in IE?). I found that 'cart' was always getting added to Drupal's cache_page table. Doesn't it make sense that it *not*? In fact, it broke checkout for our anonymous users. Try it out, let me know if it works for you. Thanks @neclimdul! Note: the fix is just the 'cart' -> drupal_page…

gistfile1.php

/**
 * Implements hook_init().
 */
function uc_cart_init() {
  global $conf;
  $conf['i18n_variables'][] = 'uc_cart_breadcrumb_text';
  $conf['i18n_variables'][] = 'uc_cart_help_text';
  $conf['i18n_variables'][] = 'uc_continue_shopping_text';

  // Don't cache any cart of checkout pages.
  // Code based on CacheExclude - http://drupal.org/project/cacheexclude
  // Thanks @neclimdul!
  if (arg(0) == 'cart') {
    drupal_page_is_cacheable(FALSE);
  }
}