Structure ComboItem
 
    Sub New(id As Integer, value As String)
        Me.Id = id
        Me.Value = value
    End Sub
 
    Property Id As Integer
    Property Value As String
 
    Overrides Function ToString() As String
        Return Value
    End Sub
 
End Structure

ComboBox1.Items.Add(New ComboItem(0, "Hallo"))
ComboBox1.Items.Add(New ComboItem(1, "Welt"))

Private Sub ComboBox1_SelectedIndexChanged(sender As Object, e As EventArgs) _
  Handles ComboBox1.SelectedIndexChanged
    MessageBox.Show(DirectCast(ComboBox1.SelectedItem, ComboItem).Id.ToString)
End Sub