How to skip cart page on woocomerce for certain products only?

You need to get the product when It is just added to cart , then check if for this product you want to redirect the cart page to checkout page . You need to change $desire_product = 'certain_product'; line on below code and It will definitely work.

add_filter( 'woocommerce_add_to_cart_redirect', 'woo_redirect_checkout' );function woo_redirect_checkout() {    global $woocommerce;    $desire_product = 'certain_product';    //Get product ID    $product_id = (int) apply_filters( 'woocommerce_add_to_cart_product_id', $_POST['add-to-cart'] );    //Check if current product is subscription    if ( $product_id == $desire_product ){        $checkout_url = $woocommerce->cart->get_checkout_url();        return $checkout_url;        exit;    } else {        $cart_url = $woocommerce->cart->get_cart_url();        return $cart_url;        exit;    }}

I wrote a little plugin for this, sharing it here. The plugin adds a small checkbox to the product metabox, so you can specify which products should trigger the automatic skip to checkout. Basically using the same woocommerce_add_to_cart_redirect filter as in the other answers, but providing the admin backend option to determine which products trigger the redirection.

<?php/** * Plugin Name: Redirect to checkout * Plugin URI: http://stackoverflow.com/q/32962653/383847 * Description: redirect to checkout for certain products  * Version: 1.0 * Author: Kathy Darling * Author URI: http://kathyisawesome.com * Requires at least: 3.8 * Tested up to: 3.9 * * Text Domain: kia-redirect-to-checkout * Domain Path: /languages/ * */if ( ! defined( 'ABSPATH' ) ) {    exit; // Exit if accessed directly}/** Add text inputs to product metabox*/function kia_add_to_wc_metabox(){    global $post;    echo '<div class="options_group">';    // Suggested Price    echo woocommerce_wp_checkbox( array(        'id' => '_redirect_to_checkout',        'label' => __( 'Redirect to checkout', 'kia-redirect-to-checkout' ) ,        'description' => __( 'When this item is added to the cart, re-direct the customer to checkout immediately.', 'kia-redirect-to-checkout' )        )    );    echo '</div>';}add_action( 'woocommerce_product_options_general_product_data', 'kia_add_to_wc_metabox' );/* * Save extra meta info */function kia_process_wc_meta_box( $post_id, $post ) {    if ( isset( $_POST['_redirect_to_checkout'] ) ) {        update_post_meta( $post_id, '_redirect_to_checkout', 'yes' );    } else {        update_post_meta( $post_id, '_redirect_to_checkout', 'no' );    }}add_action( 'woocommerce_process_product_meta', 'kia_process_wc_meta_box', 1, 2 );/* * Redirect to checkout */function kia_add_to_cart_redirect( $url ){    // If product is one of our special types    if ( is_numeric( $_REQUEST['add-to-cart'] ) && kia_maybe_redirect_cart( (int) $_REQUEST['add-to-cart'] ) ) {        // Remove default cart message        WC()->clear_messages();        // Redirect to checkout        $url = WC()->cart->get_checkout_url();    }    return $url;}add_filter( 'woocommerce_add_to_cart_redirect', 'kia_add_to_cart_redirect' );/* * check if an item has custom field */function kia_maybe_redirect_cart( $product_id ){    if ( 'yes' == get_post_meta( $product_id, '_redirect_to_checkout', true ) ){        return TRUE;    } else {        return false;    }}

Updating WooCommerce 3.0+

<?php/** * Plugin Name: WC Redirect to checkout * Plugin URI: http://stackoverflow.com/q/32962653/383847 * Description: Redirect to checkout for certain products  * Version: 1.0 * Author: Kathy Darling * Author URI: http://kathyisawesome.com * Requires at least: 3.8 * Tested up to: 3.9 * WC requires at least: 3.1.0 * WC tested up to: 4.0.1 * * Text Domain: kia-redirect-to-checkout * Domain Path: /languages/ * */if ( ! defined( 'ABSPATH' ) ) {    exit; // Exit if accessed directly}/** * Add text inputs to product metabox */function kia_add_to_wc_metabox(){    global $post;    echo '<div class="options_group">';    // Suggested Price    echo woocommerce_wp_checkbox( array(        'id' => '_redirect_to_checkout',        'label' => __( 'Redirect to checkout', 'kia-redirect-to-checkout' ) ,        'description' => __( 'When this item is added to the cart, re-direct the customer to checkout immediately.', 'kia-redirect-to-checkout' )        )    );    echo '</div>';}add_action( 'woocommerce_product_options_general_product_data', 'kia_add_to_wc_metabox' );/** * Save extra meta info * * @param  WC_Product  $product */function kia_process_wc_meta_box( $product ) {    if ( isset( $_POST['_redirect_to_checkout'] ) ) {        $product->update_meta_data( '_redirect_to_checkout', 'yes' );    } else {        $product->update_meta_data( '_redirect_to_checkout', 'no' );    }}add_action( 'woocommerce_admin_process_product_object', 'kia_process_wc_meta_box' );/** * Redirect to checkout * * @param  WC_Product  $product */function kia_add_to_cart_redirect( $url, $product ) {    // If product is one of our special products.    if ( kia_maybe_redirect_cart( $product ) ) {        // Remove default cart message.        wc_clear_notices();        // Redirect to checkout.        $url = wc_get_checkout_url();    }    return $url;}add_filter( 'woocommerce_add_to_cart_redirect', 'kia_add_to_cart_redirect', 10, 2 );/** * Check if an item has custom field. * * @param  WC_Product  $product */function kia_maybe_redirect_cart( $product ) {    return wc_string_to_bool( $product instanceof WC_Product && $product->get_meta( '_redirect_to_checkout', true ) );}

https://gist.github.com/helgatheviking/f76b97d7d19813538e32b8f5f2dae6ec

There are a few action hooks as well that you can use, for eg: woocommerce_add_to_cart which passes the product id to the callback function:

add_action( 'woocommerce_add_to_cart', 'custom_add_to_cart', 10, 2 );function custom_add_to_cart( $cart_item_key, $product_id ) {    // replace 123 with a valid product id    if( 123 == $product_id ) {        wp_redirect( WC()->cart->get_checkout_url() );        exit;       }}