A thicker swim cap (made of silicon as opposed to latex) might be preferable to keep the head warmer. Sometimes a swimming cap does not stay on very well and continually slips. This can be extremely annoying during a race. Try wearing a new cap which isn't stretched out. Another tip, avoid hair conditioner for several days before a race. Conditioner makes the hair slippery and helps the cap slide. If the water and air are hot, and your hair short, a cap may not be necessary.
Tinted goggles which reflect the sun and reduce glare can also be helpful, but they are not a necessity. Make sure your goggle strap is properly adjusted, and you may want to use an anti-fog coating or a bit of saliva to avoid cloudy lenses.
A special swimming suit is not necessary although chaffing is a consideration when selecting your attire. Rub marks on the skin from the suit and body parts can occur and are likely in salt water. The more salt, the more rubs. When I swam a 12 mile race around Key West, the water was so salty that all of the seams of my suit created rub marks which was very unusual. Rub areas include the armpit, inner thighs, neck and bust line. Women have more trouble because of their suits at the neck and bust line near the armpit. Men can have trouble where their beard or whiskers rub against their neck and arms. If you are wearing a suit which zips up the back, the zipper at the top often rubs the skin. Sewing a small piece of felt or chamois cloth between the zipper closure and skin will prevent chaffing.
Vaseline, lanolin, bag balm or other grease can be used to prevent chafe marks. Now that I've had a baby, I suspect that "Desitin" would also work well, but I haven't tried it yet. For beginners, apply grease in the armpit, neck and inner thigh. If rubs are going to occur in other areas, a few training swims will make bring them to the forefront. Some swimmers use gloves, a rag or even a stick off the beach to apply grease without getting it on their hands. Grease on the hands can easily get on goggles. Greasy goggles, not good!
Also, don't forget sunblock if you are out during peak sun hours. Experiment and find out what works best for your skin. Waterproof does not necessarily mean that the block will work for hours on end. If you are planning a long training swim, try to start early in the morning before the sun's rays reach their peak.