02-add-custom-user-input-woocommerce-product.php

<?php
add_filter( 'woocommerce_add_cart_item_data', 'add_cart_item_data', 10, 2 );
/**
 * Add sem-ad-budget field value to the cart item data.
 *
 * @param array $cart_item_data Data for cart item.
 * @param int $product_id The product ID.
 */
public function add_cart_item_data( $cart_item_data, $product_id ) {
	global $woocommerce;

	// Check if value was posted then set cart item meta.
	if ( isset($_POST[ 'sem-ad-budget' ]) ) {
		$cart_item_data['sem-ad-budget'] = $_POST['sem-ad-budget'];
	}
	return $cart_item_data;
}

add_filter( 'woocommerce_get_cart_item_from_session', 'get_cart_items_from_session', 1, 3 );
/**
 * Get sem-ad-budget cart meta value and add to session data.
 *
 * @param  array $session_data Item to add value to. 
 * @param  array $values Cart key values.
 * @param  string $key Cart key.
 * @return array $session_data The item.
 */
public function get_cart_items_from_session( $session_data, $values, $key ) {
	// Check if value is in cart values then add to session_data.
	if ( array_key_exists( 'sem-ad-budget', $values ) ) {
		$session_data[ 'sem-ad-budget' ] = $values['sem-ad-budget'];
	}

	return $session_data;
}

add_filter( 'woocommerce_get_item_data', 'display_ad_budget_in_cart', 10, 2 );
/**
 * Add and display sem-ad-budget $item meta to cart $data array.
 *
 * @param  array $data Data for all cart items.
 * @param  array $item The item.
 * @return array $data Data for all cart items.
 */
public function display_ad_budget_in_cart( $data, $item ) {
	// Check if item meta is set then add to cart data array.
	if ( isset( $item['sem-ad-budget'] ) ) {
		$data[] = array(
			'name' => 'Monthly Ad Budget',
			'value' => '$' . $item['sem-ad-budget']
		);
	}
	return $data;
}