You have a choice of a seatpost-clamping rack or one using the wheel quick-release and the seatpost collar as mounting points. You can't use P clips on a carbon frame.
Seatpost racks need a beefy metal post so replace the carbon one with a midrange aluminium, nothing ultralight. The racks come with a low max load, maybe two small panniers.
Another alternative is a large Carradice saddlebag, with a barbag up front.