Tell the user which product the quantity is for. Your code will not pull data from each column of the selected items. Review http://allenbrowne.com/ser-50.html
Code:
Dim varItem As Variant
Dim ctl As Control
Set ctl = Me.List0ne
For Each varItem In ctl.ItemsSelected
rs!.AddNew
rs![Category ID] = ctl.Column(0, varItem)
rs![Product Name] = ctl.Column(1, varItem)
rs!OtherValue = InputBox("Enter a Numeric Quantity for product " & ctl.Column(1, varItem))
Next
You don't show code to declare, set, open recordset - assume you do have that in procedure.