1) Sunscreen. forgot that once and got fried
2) Get a tub to store all your bits in. That way you should never forget stuff unless to forget to pack the tub
3) Buy a new universal joint every season (dependent on season use so maybe every second), it's like an insurance policy. Cheaper than losing a rig if your trusty old one breaks. It was suggested to me by an old sailor who broke one a long way from home and lost ALL his kit, had a very long frightening swim.
4) Guy Cribb intuition course....worth it
5) Small esky for beers (as mentioned a few times) Salt with a beer chaser

. Not too many beers remember you need to drive home to your family and return to the beach for the next session