Visual Basic.NET - Duda con Combobox

Public Conexion As String = "Data Source=.\SQLEXPRESS;Initial Catalog=Construccion;Integrated Security=True"

    Public MiConexion As New SqlConnection(Conexion)

    Public Rs As SqlDataReader

    Public Com As New SqlCommand

    Public SQL As String

Public Sub Zonas()

        Sql = "select CodZona,Descripcion from Zonas"

        Com = New SqlCommand(Sql, MiConexion)

        Rs = Com.ExecuteReader()

        While Rs.Read()

            cboZona.Items.Add(Rs("Descripcion"))

            Microsoft.VisualBasic.Compatibility.VB6.SetItemData(cboZona, cboZona.Items.Count - 1, Rs("CodZona"))

        End While

        cboZona.Items.Add("Otra Zona")

        Rs.Close()

        Cerrar()

    End Sub

 Public Sub Cerrar()

        Rs = Nothing

        Com = Nothing

    End Sub