Easily Offer Free or Paid Add-ons and Services at Checkout. The core WooCommerce checkout process covers all of the basic fields shops needs to place an order, but what if your shop needs to offer services or additional products only at checkout? That's where WooCommerce Checkout Add-ons comes into play. This extension allows you to add several additional options to your checkout page and determine which are free or paid. You can also sort and filter orders based on your shiny new options.