If you want to add or change the checkout summary section, you can proceed creating a module with a plugin, like this:

• app/code/Offset101/AttributeCheckout/registration.php
  
  1 2 3 4 5 6 7

  <?php \Magento\Framework\Component\ComponentRegistrar::register(     \Magento\Framework\Component\ComponentRegistrar::MODULE,     'Offset101_AttributeCheckout',     __DIR__ );

• app/code/Offset101/AttributeCheckout/etc/di.xml
  
  1 2 3 4 5 6 7 8

  <?xml version="1.0"?>   <config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"         xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">     <type name="Magento\Checkout\Model\DefaultConfigProvider">         <plugin name="AddAttPlug" type="Offset101\AttributeCheckout\Plugin\ConfigProviderPlugin" />     </type> </config>

• app/code/Offset101/AttributeCheckout/etc/module.xml
  
  1 2 3 4 5 6

  <?xml version="1.0"?>   <config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Module/etc/module.xsd">     <module name="Offset101_AttributeCheckout" setup_version="1.0.0">     </module> </config>

• app/code/Offset101/AttributeCheckout/Plugin/ConfigProviderPlugin.php
  
  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

  <?php   namespace Offset101\AttributeCheckout\Plugin;   class ConfigProviderPlugin extends \Magento\Framework\Model\AbstractModel {       public function afterGetConfig(\Magento\Checkout\Model\DefaultConfigProvider $subject, array $result)     {        $items = $result['totalsData']['items'];     // Your logic here - for each added product         foreach($items as $idx => $item){             $options = json_decode($items[$idx]['options']);               $output = "";             foreach($options as $option){                 $output .= $option->label.' - '.strip_tags($option->value);             }       // New attribute to add             $items[$idx]['checkoutItems'] = $output;         }   // Update the items array         $result['totalsData']['items'] = $items;         return $result;     }   }

  
   
• Then, you will need to override the following phtml in your custom theme app/design/frontend/<your_theme>/blank/Magento_Checkout/web/template/summary/item/details.html  Adding your new field, below the name, like this:
  
  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

  <!-- /** * Copyright © 2013-2017 Magento, Inc. All rights reserved. * See COPYING.txt for license details. */ -->   <!-- ko foreach: getRegion('before_details') -->     <!-- ko template: getTemplate() --><!-- /ko --> <!-- /ko --> <div class="c-minicart__info">     <div class="top-content_minicart">         <div class="info-content">             <p class="c-minicart__highlight" data-bind="text: $parent.name"></p>             <p class="c-minicart__highlight" data-bind="text: $parent.checkoutItems"></p>     <!-- New field -->         </div>     </div>

• Afterwards, remember to:
  
  1 2 3 4 5 6

  php bin/magento module:enable Offset101_AttributeCheckout php bin/magento setup:upgrade php bin/magento setup:di:compile php bin/magento indexer:reindex php bin/magento setup:static-content:deploy -f php bin/magento cache:flush