I have successfully setup some custom fields on checkout and it all works fine.

I have a checkbox as one of the fields, my_gift_wrap_checkbox, and I managed to write code to display text in the orders page ('yes please!' or 'no thank you') instead of a simple blank or 1 if it is checked or not.

I can't figure out how to achieve the same in the email code. My code is:

/**
 * Add the field to order emails
 **/
add_filter('woocommerce_email_order_meta_keys', 'my_woocommerce_email_order_meta_keys');

function my_woocommerce_email_order_meta_keys( $keys ) {
    $keys['Gift wrap?'] = 'my_gift_wrap_checkbox';
    $keys['Gift wrap instructions'] = 'my_gift_wrap_field';
    return $keys;
}

Right now:

• If it's checked, I get Gift wrap?: 1
• I want Gift wrap?: Yes please!
• If it's not checked, it shows Gift wrap?:
• I want Gift wrap?: No thank you.