MS Access: Display two columns in combo-box

It depends to a certain extent on what you are doing, often something like this suits:

SELECT Id, Surname & ", " & Forename from Table

In other words, the bound column is a unique ID and the selection column includes both the surname and forename in a single column.

EDIT based on additional information:

SELECT [Contact].[CID], [Contact].[Csname] & ", " & [Contact].[Cfname] 
FROM [Contact] ORDER BY [CID], [Csname], [Cfname];