Warm Outerwear - Paddling Parkas, Fleece Ponchos, and warm hat
Put something on right after you get out of the water
If you aren't changing into dry clothes, a long poncho, parka or robe can keep your car seat from getting wet and keep you warmer.
Warm drink - soup, cocoa, etc. in a thermos will help warm you up
Additional snack - energy bar, etc. for quick energy boost to help body heat generation
Car idling used as a luxury isn't a great practice given climate change concern, but if you are really cold - crank up the car heater and get warm.
Getting Out Of Your Paddling Gear - if you are going to change clothes before going home
Bring a change of dry clothes in the car
Foam Pad to Stand on - warmer, more comfortable to stand on, protect the gear you are getting out of - keep your wetsuits clean, minimize wear from contact with rough surfaces
No Changing Room? you can use a towel or that warm paddle robe or poncho you already put on for privacy.