Re: Do you wear a life jacket?
Like others, I always wear my Auto Mustang. I use the harness when I am sailing solo, or out of the Golden Gate (which equate to open ocean for me), or in rough weather.
If you have any doubts about this, look at reports of boating accidents and fatalities. In almost every fatality the person was not wearing a lifejacket. Especially among powerboat users, and jetski users.
A life jacket is essential!
As for essential devices, that is a rather open-ended question; it depends on the boat you are in (rowboat, 54 footer, etc). A good place to start is the USCG which mandates minimal safety equipment (e.g. flares, horns, etc). We can suggest others. depending on your situation.....