Module is released in drupal.org, get the updated recent code from https://www.drupal.org/project/basic_cart
Basic Cart Drupal 8
Basic cart is a very simple shopping cart / checkout process for Drupal, that just sends 2 emails after each order. Along with the shopping cart, this module also provides a block where you can view your cart's content. It's ideal for small websites with only a few products or other content types being sold, for example touristic offers.
Usage
Install the module. If the goods you want to sell don't exist on your website, create a new content type for them. If you already have a content type for them you can skip this step. Select the content type/s on the module configuration page: Configuration - Basic Cart or admin/config/basic_cart. Create a view for the content type/s to get the shop's overview. If you already have it, you can skip this step. You have a block with the cart preview. Activate it ;-) Start to add you're products in the newly created content type or in the one you already have.