title: Woocommerce custom cart input fields
body: <p>I want to add extra input fields to woocommerce cart page, yet I found one hook <code>woocommerce_proceed_to_checkout</code> of cart page.</p>
  
  <p>I also have to update and get values of custom fields, I have questions:</p>
  
  <p>1) How to save <code>datepicker_checkout</code> input field?</p>
  
  <p>2) How to get value of this field when I calling <code>insert_input_text_to_checkout</code> function from <code>woocommerce_proceed_to_checkout</code> hook?</p>
  
  <p><strong>This code is only add an extra to cart page:</strong></p>
  
  <pre><code>add_action( 'woocommerce_proceed_to_checkout', 'insert_input_text_to_checkout' );
  function insert_input_text_to_checkout($checkout)
  {
      woocommerce_form_field( 'datepicker_checkout', array
      (
          'type'         =&gt; 'text',
          'class'         =&gt; array('my-field-class form-row-wide'),
          'id'            =&gt; 'datepicker_checkout',
          'label'         =&gt; __('Select Date'),
          'placeholder'   =&gt; __('dd/mm/yyyy'),
          'required'     =&gt; true,
      )/*, how to get value of 'datepicker_checkout' ? */);
  }
  </code></pre>