If you were out hiking, you would take your cell phone, water and a first aid kit. So what would you take if you were going out on a boat? One handy item is a pocket knife and keep it in your pocket. I am not talking about a utility knife that you open boxes with but a study knife capable of cutting through ropes.
Don't keep the pocket knife in your purse or bag, you need to keep it on you. If you fall overboard and should need it, you have it with you. Nothing worse than bringing something you need on a trip and getting separated from it when you need it the most.