Using the Open event would be better, here is the general syntax for an example, modify for parent sheet name, combobox name, and the "few items" you want to populate the combobox with.
Private Sub Workbook_Open()
With Worksheets("Sheet1").OLEObjects("ComboBox1").Object
.Clear
.AddItem "Value 1"
.AddItem "Value 2"
.AddItem "Value 3"
.ListIndex = 0 'optional
End With
End Sub
Make sure the ListFillRange property of the combobox is empty.
Place the code in your workbook module and see if it accomplishes what you are after. To easily access your workbook module, find the little Excel workbook icon near the upper left corner of your workbook window, usually just to the left of the File menu option. Right click on that icon, left click on View Code, and paste the above procedure into the large white area that is the workbook module. Press Alt+Q to return to the worksheet.
After that, save the workbook, close it, and when you reopen it the values will be populated into the combobox as the code suggests.