Adding Numbers To Rows Using A Command Button ()

I have a user form with combo boxes. The user selects items from the combo box and when they click the command button the selection is written to the spreadsheet. Each time the button is clicked it adds an item to the sheet making a list of items. I am trying to assign a number to each item when the command button is clicked so I have numbered list. Here is my code so far:

Private Sub cmdbtnAdd_Click()

Dim RowCount As String

'Writes user inputs to Active Worksheet when Add Item Button is clicked.

RowCount = Worksheets("Sheet1").Range

("A1").CurrentRegion.Rows.Count

With Worksheets("Sheet1").Range("A1")

.Offset(RowCount, 0).Value = ' This is where I have been trying to code in the numbering

.Offset(RowCount, 1).Value = Me.Combobox1

.Offset(RowCount, 2).Value = Me.ComboBox2

End With

End Sub