You can specify the menu items using Items/MenuItems property.

See also the list of supported menu actions.

ASP.NET WebForms

.aspx

<daypilot:daypilotmenu id="DayPilotMenu1" runat="server" ClientObjectName="menu">
  <DayPilot:MenuItem Text="Open" Action="JavaScript" JavaScript="alert('Opening event (id ' + e.value() + ')');" ></DayPilot:MenuItem>
  <DayPilot:MenuItem Text="-" Action="NavigateUrl" ></DayPilot:MenuItem>
  <DayPilot:MenuItem Text="Delete (CallBack)" Action="CallBack" Command="Delete"></DayPilot:MenuItem>
  <DayPilot:MenuItem Action="PostBack" Command="Delete" Text="Delete (PostBack)" />
  <DayPilot:MenuItem Text="Delete (JavaScript using callback)" Action="JavaScript" Command='Delete' JavaScript="if (confirm('Do you really want to delete event ' + e.text() + ' ?')) ctl00_ContentPlaceHolder1_DayPilotCalendar1.eventMenuClickCallBack(e, command);"></DayPilot:MenuItem>
</daypilot:daypilotmenu>

Code behind (C#)

protected void Page_Load(object sender, EventArgs e)
{
  DayPilotMenu1.MenuItems.Clear();

  // <DayPilot:MenuItem Text="Open" Action="JavaScript" JavaScript="edit(e);" ></DayPilot:MenuItem>
  MenuItem open = new MenuItem();
  open.Text = "Open";
  open.Action = MenuItemAction.JavaScript;
  open.JavaScript = "edit(e);";
  DayPilotMenu1.MenuItems.Add(new MenuItem());
  // ...

}

ASP.NET MVC

@Html.DayPilotMenu("menu1", new DayPilotMenuConfig
{
  Items = new DayPilot.Web.Mvc.MenuItemCollection()
  {
      new DayPilot.Web.Mvc.MenuItem { Text = "Open", Action = MenuItemAction.JavaScript, JavaScript = "alert(e.value());"},
      new DayPilot.Web.Mvc.MenuItem { Text = "Delete", Action = MenuItemAction.CallBack, Command = "Delete"}
  }
})

JavaScript

dp.contextMenu = new DayPilot.Menu({
  items: [
  {text:"Show event ID", onclick: function() {alert("Event value: " + this.source.value());} },
  {text:"Show event text", onclick: function() {alert("Event text: " + this.source.text());} },
  {text:"Show event start", onclick: function() {alert("Event start: " + this.source.start().toStringSortable());} },
  {text:"Delete", onclick: function() { dp.events.remove(this.source); } }
]});