Hoods - Since it's a well known fact that over 70% of your body heat 'escapes' through your head it’s advised to consider a hood for diving in water temperatures below 70 degrees F. In the underwater environment that issue still applies. These accessories will give your head thermal protection from the cold, along with protection from coral and other sharp objects.
Gloves - Protection from the elements is a key when it comes to scuba gloves. Your hands may become soft from extended exposure to the water and cut or scraped easily. Cold water will numb your hands and make it hard for you to operate your equipment. These accessories will give your hands thermal protection from the cold, along with protection from coral and other sharp objects.
Boots - Protection against cuts and abrasions as well as heat loss will be prevented by acquiring a pair of diving boots. They also allow for more effective control with water propulsion using your fins. Like air temperature, water temperatures throughout the world are different in winter than they are in summer, varying as much as 20 degrees. If in doubt, always buy a boots slightly warmer than your needs. Your feet will never get too warm, but if you are cold during a dive there is not much you can do except stop diving.
Alternate Air Sources - Commonly referred to as the octopus or 'octo'. This is your backup second stage regulator. It works just the same as the primary second stage regulator and can be used in the unlikely event that your primary fails or your dive buddy needs to share air. This accessories usually a bright color such as fluorescent yellow or pink and is normally secured somewhere within the triangle between the chin and the bottom of the rib cages, normally on the right side.
Compass - During underwater, it is easy to loose your sense of direction, specifically in bad visibility or unfamiliar surroundings. Using these accessories as reference will assist in many a sticky situation.
Thermometer - Not an essential accessory, but these accessories does come in handy when monitoring your temperature in accordance with depth and time in the water during diving.
Scuba Weights - The purpose of these accessories in diving is not to make you sink, but to ensure that you maintain buoyant with all the floatation and warmth-inducing devices required for the dive. Weight belts are available as a separate fixture or integrated into the BCD or suit.
Underwater Cameras - Underwater photography is the process of taking photographs while under water by using waterproof underwater camera. It is usually done while scuba diving, but can be done while snorkeling or swimming. This is an additional accessories for underwater but more meaningful.