Ben, I don't go anywhere without the following - in dddition to the obvious!
1) 2 pairs of gloves (you can rotate them so you are not wearing stinky wet golves all the time)
2) Split ring pliers, preferably in a holster on the gimbal belt
3) Braid scissors
4) Lighter - for burning over the ends of knots (don't rely on smokers being on board)
5) Buff / hat (or other preffered form of sun protection) + suntan lotion.
6) Spare spools with leaders tied already to go, it's a lot quicker than re tying a leader after a bust off during a hot bite - you can do that over evening drinks.
7) A pocket pull of something sugary, like snakes or jelly beens for when you think you are about to hit the wall!
and finally
A pair of swimmers to cool off when the bite shuts down!
Cheers.