PFDs must be approved by the United States Coast Guard. To see the kinds of PFDs available, look here . In addition, if your boat is 16 feet or over, you need to have a throwable PFD onboard, and immediately available, in case someone falls overboard. You already know that you should wear your PFD whenever you are underway. In many states, the law says you must wear your PFD when underway or when on a PWC or water skiing, etc.
Every boat needs a working whistle or horn to make sound.
Boats over 30 feet have additional requirements you can find on the printable Required Equipment Chart . You can attach a whistle to your PFD so that you always have a sound producing device within reach . Make sure it is a whistle that works when it gets wet. Remember - only use it in a real emergency. To see a chart of visual distress signals, click here .