Add a custom bookmarks MultiItem to the ToolbarControl
MultiItemBookmarks.cs
// Copyright 2012 ESRI
// 
// All rights reserved under the copyright laws of the United States
// and applicable international laws, treaties, and conventions.
// 
// You may freely redistribute and use this sample code, with or
// without modification, provided you include the original copyright
// notice and use restrictions.
// 
// See the use restrictions.
// 

using System;
using System.Drawing;
using System.Collections;
using System.ComponentModel;
using System.Windows.Forms;
using System.Data;
using ESRI.ArcGIS.Controls;
using ESRI.ArcGIS.SystemUI;
using ESRI.ArcGIS;


namespace MultiItemBookmarks
{

  public class Form1 : System.Windows.Forms.Form
  {
    public System.Windows.Forms.Label Label4;
    public System.Windows.Forms.Label Label3;
    public System.Windows.Forms.Label Label1;
    public System.Windows.Forms.Label Label2;
    private ESRI.ArcGIS.Controls.AxToolbarControl axToolbarControl1;
    private ESRI.ArcGIS.Controls.AxMapControl axMapControl1;
    private ESRI.ArcGIS.Controls.AxLicenseControl axLicenseControl1;

    private System.ComponentModel.Container components = null;

    public Form1()
    {

      InitializeComponent();

    }

    protected override void Dispose( bool disposing )
    {
            ESRI.ArcGIS.ADF.COMSupport.AOUninitialize.Shutdown();
      if( disposing )
      {
        if (components != null) 
        {
          components.Dispose();
        }
      }
      base.Dispose( disposing );
    }

    #region Windows Form Designer generated code
    /// <summary>
    /// Required method for Designer support - do not modify
    /// the contents of this method with the code editor.
    /// </summary>
    private void InitializeComponent()
    {
      System.Resources.ResourceManager resources = new System.Resources.ResourceManager(typeof(Form1));
      this.Label4 = new System.Windows.Forms.Label();
      this.Label3 = new System.Windows.Forms.Label();
      this.Label1 = new System.Windows.Forms.Label();
      this.Label2 = new System.Windows.Forms.Label();
      this.axToolbarControl1 = new ESRI.ArcGIS.Controls.AxToolbarControl();
      this.axMapControl1 = new ESRI.ArcGIS.Controls.AxMapControl();
      this.axLicenseControl1 = new ESRI.ArcGIS.Controls.AxLicenseControl();
      ((System.ComponentModel.ISupportInitialize)(this.axToolbarControl1)).BeginInit();
      ((System.ComponentModel.ISupportInitialize)(this.axMapControl1)).BeginInit();
      ((System.ComponentModel.ISupportInitialize)(this.axLicenseControl1)).BeginInit();
      this.SuspendLayout();
      // 
      // Label4
      // 
      this.Label4.BackColor = System.Drawing.SystemColors.Control;
      this.Label4.Cursor = System.Windows.Forms.Cursors.Default;
      this.Label4.Font = new System.Drawing.Font("Arial", 8F, System.Drawing.FontStyle.Regular, System.Drawing.GraphicsUnit.Point, ((System.Byte)(0)));
      this.Label4.ForeColor = System.Drawing.SystemColors.ControlText;
      this.Label4.Location = new System.Drawing.Point(456, 192);
      this.Label4.Name = "Label4";
      this.Label4.RightToLeft = System.Windows.Forms.RightToLeft.No;
      this.Label4.Size = new System.Drawing.Size(137, 49);
      this.Label4.TabIndex = 8;
      this.Label4.Text = "Create a new bookmark based on the current extent of the focus map.";
      // 
      // Label3
      // 
      this.Label3.BackColor = System.Drawing.SystemColors.Control;
      this.Label3.Cursor = System.Windows.Forms.Cursors.Default;
      this.Label3.Font = new System.Drawing.Font("Arial", 8F, System.Drawing.FontStyle.Regular, System.Drawing.GraphicsUnit.Point, ((System.Byte)(0)));
      this.Label3.ForeColor = System.Drawing.SystemColors.ControlText;
      this.Label3.Location = new System.Drawing.Point(456, 96);
      this.Label3.Name = "Label3";
      this.Label3.RightToLeft = System.Windows.Forms.RightToLeft.No;
      this.Label3.Size = new System.Drawing.Size(137, 41);
      this.Label3.TabIndex = 7;
      this.Label3.Text = "Navigate around the data using the commands on the ToolbarControl.";
      // 
      // Label1
      // 
      this.Label1.BackColor = System.Drawing.SystemColors.Control;
      this.Label1.Cursor = System.Windows.Forms.Cursors.Default;
      this.Label1.Font = new System.Drawing.Font("Arial", 8F, System.Drawing.FontStyle.Regular, System.Drawing.GraphicsUnit.Point, ((System.Byte)(0)));
      this.Label1.ForeColor = System.Drawing.SystemColors.ControlText;
      this.Label1.Location = new System.Drawing.Point(456, 144);
      this.Label1.Name = "Label1";
      this.Label1.RightToLeft = System.Windows.Forms.RightToLeft.No;
      this.Label1.Size = new System.Drawing.Size(137, 49);
      this.Label1.TabIndex = 6;
      this.Label1.Text = "Zoom to any bookmarks listed in the spatial bookmark menu.";
      // 
      // Label2
      // 
      this.Label2.BackColor = System.Drawing.SystemColors.Control;
      this.Label2.Cursor = System.Windows.Forms.Cursors.Default;
      this.Label2.Font = new System.Drawing.Font("Arial", 8F, System.Drawing.FontStyle.Regular, System.Drawing.GraphicsUnit.Point, ((System.Byte)(0)));
      this.Label2.ForeColor = System.Drawing.SystemColors.ControlText;
      this.Label2.Location = new System.Drawing.Point(456, 48);
      this.Label2.Name = "Label2";
      this.Label2.RightToLeft = System.Windows.Forms.RightToLeft.No;
      this.Label2.Size = new System.Drawing.Size(137, 40);
      this.Label2.TabIndex = 5;
      this.Label2.Text = "Browse to a map document to load into the MapControl.";
      // 
      // axToolbarControl1
      // 
      this.axToolbarControl1.Location = new System.Drawing.Point(8, 8);
      this.axToolbarControl1.Name = "axToolbarControl1";
      this.axToolbarControl1.OcxState = ((System.Windows.Forms.AxHost.State)(resources.GetObject("axToolbarControl1.OcxState")));
      this.axToolbarControl1.Size = new System.Drawing.Size(584, 28);
      this.axToolbarControl1.TabIndex = 9;
      // 
      // axMapControl1
      // 
      this.axMapControl1.Location = new System.Drawing.Point(8, 40);
      this.axMapControl1.Name = "axMapControl1";
      this.axMapControl1.OcxState = ((System.Windows.Forms.AxHost.State)(resources.GetObject("axMapControl1.OcxState")));
      this.axMapControl1.Size = new System.Drawing.Size(440, 312);
      this.axMapControl1.TabIndex = 10;
      // 
      // axLicenseControl1
      // 
      this.axLicenseControl1.Enabled = true;
      this.axLicenseControl1.Location = new System.Drawing.Point(360, 264);
      this.axLicenseControl1.Name = "axLicenseControl1";
      this.axLicenseControl1.OcxState = ((System.Windows.Forms.AxHost.State)(resources.GetObject("axLicenseControl1.OcxState")));
      this.axLicenseControl1.Size = new System.Drawing.Size(200, 50);
      this.axLicenseControl1.TabIndex = 11;
      // 
      // Form1
      // 
      this.AutoScaleBaseSize = new System.Drawing.Size(5, 13);
      this.ClientSize = new System.Drawing.Size(600, 358);
      this.Controls.Add(this.axLicenseControl1);
      this.Controls.Add(this.axMapControl1);
      this.Controls.Add(this.axToolbarControl1);
      this.Controls.Add(this.Label4);
      this.Controls.Add(this.Label3);
      this.Controls.Add(this.Label1);
      this.Controls.Add(this.Label2);
      this.Name = "Form1";
      this.Text = "Form1";
      this.Load += new System.EventHandler(this.Form1_Load);
      ((System.ComponentModel.ISupportInitialize)(this.axToolbarControl1)).EndInit();
      ((System.ComponentModel.ISupportInitialize)(this.axMapControl1)).EndInit();
      ((System.ComponentModel.ISupportInitialize)(this.axLicenseControl1)).EndInit();
      this.ResumeLayout(false);

    }
    #endregion

    [STAThread]
    static void Main() 
    {        
            
            if (!RuntimeManager.Bind(ProductCode.Engine))
            {
                if (!RuntimeManager.Bind(ProductCode.Desktop))
                {
                    MessageBox.Show("Unable to bind to ArcGIS runtime. Application will be shut down.");
                    return;
                }
            }

      Application.Run(new Form1());
    }

    private void Form1_Load(object sender, System.EventArgs e)
    {
      //Set buddy control
      axToolbarControl1.SetBuddyControl(axMapControl1);
      
      //Add command items to the ToolbarControl
      axToolbarControl1.AddItem("esriControls.ControlsOpenDocCommand", -1, -1, false, 0, esriCommandStyles.esriCommandStyleIconAndText);
      axToolbarControl1.AddItem("esriControls.ControlsMapZoomInTool", -1, -1, true, 0, esriCommandStyles.esriCommandStyleIconAndText);
      axToolbarControl1.AddItem("esriControls.ControlsMapZoomOutTool", -1, -1, false, 0, esriCommandStyles.esriCommandStyleIconAndText);
      axToolbarControl1.AddItem("esriControls.ControlsMapPanTool", -1, -1, false, 0, esriCommandStyles.esriCommandStyleIconAndText);
      axToolbarControl1.AddItem("esriControls.ControlsMapFullExtentCommand",-1 , -1, false, 0, esriCommandStyles.esriCommandStyleIconAndText);
      
      //Create a new ToolbarMenu 
      IToolbarMenu2 toolbarMenu = new ToolbarMenuClass();
      
      //Set a caption
      toolbarMenu.Caption = "Spatial Bookmarks";
      //Add the custom command to the ToolbarMenu
      toolbarMenu.AddItem(new CreateBookmark(), -1, -1, false, esriCommandStyles.esriCommandStyleTextOnly);
      //Add the custom multiitem to the ToolbarMenu
      toolbarMenu.AddMultiItem(new SpatialBookmarks(), -1, true, esriCommandStyles.esriCommandStyleTextOnly);
      
      //Add the menu item to the ToolbarControl
      axToolbarControl1.AddItem(toolbarMenu, -1, -1, true, 0, esriCommandStyles.esriCommandStyleMenuBar);
      
    }
  }
}