woocommerce-persistant-checkout-1.php

<?php
add_action( 'woocommerce_after_checkout_validation', 'set_persitent_checkout' );

function set_persitent_checkout ( $a ) 
{
    $arr = array();
    foreach ( $a as $key => $value )
        if ( ! empty($value) )
            $arr[$key] = $value;
            
    WC()->session->set( 'form_data', $arr );
    return $a;
}