If you are not a hat person, then see our recommendations for umbrellas. It is a good idea to wear a hat for general sun protection and a wide brim offers the best protection. Of course once you put the hat on, it becomes a hat day. This is because you will have hat hair, when you take it off.
You will want a high speed camera with a 1/1000 second shutter speed and at least 10X optical zoom, possibly on a tripod. Do not use digital zoom or you are sure to be disappointed. The action on the water is best captured by following a boat in the viewfinder as it goes by, and snapping the shutter while still moving the camera. This keeps the boat sharply focused, while blurring the background. Other cameras are great for pictures in the pits and the people around you.
The race teams are starting to use radios to communicate with their drivers on the race course. You might be able to listen in on them. If you see someone in a racing uniform with a headset and a microphone, do not distract them during the race. However, most are friendly people are will be glad to tell you about their boats.
These are not necessary, but are great for peering into the pits and people watching.
Books, Magazines, Cards, Headset
Entertaining yourself and your family between the events on the water can make the day more enjoyable for some.