This plugin adds a script that will save checkout form field values in browser storage. The values persist on a refresh, leaving the site and coming back later, or if there is an error on submission.

Just a proof of concept, not production ready.

Read the full post at https://hollerwp.com/save-woocommerce-checkout-form-values/

Update 3/15/21: Move email field first and save the email after it is filled in. Can be used to email the customer if the checkout is abandoned. See https://hollerwp.com/woo-checkout-save-email/