There are several good reasons to keep a leash at the top of your paddle boarding accessories list.
First and foremost, SUP board leashes keep you from getting accidentally separated from your board. Things happen out there on the water. A gust of wind, an unexpected wave, or a hard wake line can catch you off guard, and the next thing you know, you are swimming after a board that is drifting away faster than you can stroke. If the water is cold, the breeze stiff, or the current strong you can very quickly find yourself in distress, with only your personal flotation device (PFD) to help you as you wave bye-bye to your board.
The security of knowing that you can not be separated from safety gives you the freedom to pursue fun. Fun is a lot more fun if you don't have to worry about losses. That includes loss of your board, your gear, or your life.
Choosing the right sup paddleboard leash depends on your water style and skill level. The leash should be about one foot longer than your board and have a minimum of one swivel hook and an inline swivel to keep it from tangling.
It may be attached at the ankle, or just below the knee. Some find that attaching the leash just below the knee offers them a stronger stance, others find that it keeps them off balance. The ankle attachment allows for better kicking ability if you need to swim to safety.
When you are shopping for sup paddleboard accessories, be sure you think safety first. That goes for your pets and your gear, too. There is a wide variety of equipment that you can attach to, or use with, your paddle board, including fishing accessories and pads to keep your dog on board and your board free of claw marks. There are drink holders, tie downs, and cargo nets to keep your stuff secure.
The only paddle boarding accessories more important than leashes are Personal Floatation Devices (PFDs). There are several styles to choose from so there is no excuse not to wear one. If you are outside the official boundaries of "bathing waters", it is required by law. The bulky Type II Coast Guard approved life vest is cheap and effective. For a few dollars more, you can invest in a Type III, which exceeds Coast Guard regulations for personal flotation devices, or you can purchase an inflatable belt or vest style that can be blown up with CO2 or by breath.
Other sup paddleboard accessories should include a waterproof bag to keep your keys and ID dry and handy. Be sure you attach it to yourself, not the dog.