Gloves
Your hands are permanently in the wind and permanently wet, which makes them the first thing to go numb. Neoprene gloves and mitts from Mystic and ION, in 2mm through 5mm.
Full-finger gloves are the standard choice and the best balance of warmth and bar feel. Pre-curved designs reduce hand fatigue over long sessions, since you are not fighting the neoprene to keep a grip. Mitts are warmest by a clear margin but cost you significant feel on the bar, so most kiters only reach for them on the coldest days.
Thinner gloves preserve dexterity for adjusting your trim and quick release. Anything above 4mm makes fine adjustments genuinely difficult.