Example function getting field data from the order

pewc_attach_images_to_email.php

<?php
/**
 * Optionally attach uploaded images to the order email
 */
function pewc_attach_images_to_email( $attachments, $id, $order ) {

	if( ( $id == 'new_order' || $id == 'customer_on_hold_order' ) && get_option( 'pewc_email_images', 'no' ) == 'yes' ) {

		// Find any attachments
		$order_items = $order->get_items( 'line_item' );
		if( $order_items ) {
			foreach( $order_items as $order_item ) {
				$product_extras = $order_item->get_meta( 'product_extras' );
				if( ! empty( $product_extras['groups'] ) ) {
					foreach( $product_extras['groups'] as $group ) {
						foreach( $group as $item_id=>$item ) {
							if( ! empty( $item['file'] ) ) {
								$attachments[] = $item['file'];
							}
						}
					}
				}
			}
		}

	}

	return $attachments;

}
add_filter( 'woocommerce_email_attachments', 'pewc_attach_images_to_email', 10, 3 );