Mostly laminates in later days, always including a dining car. Possibly the odd Park Royal or old Bredin. I never saw a Craven in one, as suggested by others - however, the odd one may have made an appearance. In earlier "CIE green" days, as mentioned already, old wooden carriages usually ex-GSWR were used.
There were specially converted "radio studio coaches" with numbers prefixed "RS". Obviously, a radio studio had to be in each train.
Long after the demise of the radio train, at least one RS appeared in the consist of one of the Connolly - Dundalk local sets, as they were so chronically short of stock. (They had SOME seats!). I took a pic of a dining car, shutters down, in one of those sets too - same reason.