Custom MetaBox : Food Menu Item Available Dates

If you have created you custom post type you can add the metabox like this:

add_action( 'add_meta_boxes', 'add_dates' );

function add_dates() {
    add_meta_box('date_select', 'Dates', 'date_select', 'customposttype', 'side', 'default');
}

function date_select() {
    global $post;
    echo '<input type="hidden" name="date_select_meta_noncename" id="date_select_meta_noncename" value="' .
    wp_create_nonce( plugin_basename(__FILE__) ) . '" />';
    $gender = get_post_meta($post->ID, '_date', true);

    // Insert checkboxes HTML
}

Then you need to save the custom meta data.

function save_dates($post_id, $post) {

    if ( !wp_verify_nonce( $_POST['date_select_meta_noncename'], plugin_basename(__FILE__) )) {
        return $post->ID;
    }

    if ( !current_user_can( 'edit_post', $post->ID ))
        return $post->ID;

    $date_meta['_date'] = $_POST['_date'];

    foreach ($date_meta as $key => $value) { 

        if( $post->post_type == 'revision' ) return; 
        $value = implode(',', (array)$value);         
        if(get_post_meta($post->ID, $key, FALSE)) {
            update_post_meta($post->ID, $key, $value);
        } else {
            add_post_meta($post->ID, $key, $value);
        }        
        if(!$value) delete_post_meta($post->ID, $key); 
    }
}

add_action('save_post', 'save_dates', 1, 2);

Of course you will need to set it up for you custom post type.

(Caveat: not tested)