Life Jacket.
       You are required by law to carry one personal flotation device (PFD), for each person on board. It's a good idea if small boat sailors wear their Pfd's at all times. Also carry a throwable cushion or life ring.
       Refreshments.
       Water and food. The sun and saltwater causes the body to need more water. I usually fill a plastic jug and freeze it. When the ice melts you'll enjoy a cool drink.
       Bailer.
       You should have a way to empty water from your boat. A one gallon milk bottle with the bottom cut out makes a great bailer.      Secure the bailer with light line so you won't lose it overboard.
       Dock Lines.
       The dock line can also be used to bring someone back onboard or can be used to replace broken rigging.
       A Whistle.
       US Coast Guard says all boats must have some effective means of making noise. Secure the whistle to your life jacket.
       Tools.
       Take on board a canvas bag with a marlinspike knife, screwdriver, pliers, duct tape, small line, a few spare shackles, tack pins, and a small first aid kit, along with sunscreen and chapstick.
       Navigation Tools.
       Wristwatch and compass. The watch will help you to know when you should return for home and the compass will help you if an unexpected fog rolls in.  Make sure you know where you are at all times. If an emergency does arise you will know immediately how to return home.
       Paddle.
       If the wind dies, the paddle will help you return to shore.
       Marine Clothing.
       It is usually cooler on the water than on land. Bring adequate clothing for protection. There's nothing worse than being cold and wet when you're off shore.  Also bring sunglasses with a neck strap to protect your eyes from the sun and the reflection off the water.