For perimeter line, I use the buntline hitch for connection to deck fittings:
Perimeter line should be slightly loose while paddling, so you can get your hand, possibly gloved, around it easily. Off the water, one of the hitches can be slid to tighten the perimeter line during transport, to keep the line from flapping around in the wind on top of the car.
Rescue / Throw Bags
Gedi Convertible Helmet
Cartop Kayak Carriers