Essential gear to bring on a boating trip is like beauty – it depends on the eye of the beholder. You may not want to step off the dock without a double pack of light beer, while your wife would really like to take the kitchen sink. But probably there is a middle ground where we all can agree that some things are really necessary.
First of all, to be safe, every passenger should have true boating shoes. This term is not equivalent to sneakers, no matter how many cute little nautical flags are used for decoration. Boating shoes, in the modern, commercial sense, have grip pads or other carefully designed features on the soles to make them cling to wet, smooth surfaces. All boat decks are smooth, for maintenance reasons as well as for traditional ideas of beauty. All boat decks are very likely to get and/or stay wet.
Secondly, giving the nod to conventional medical wisdom, you should take sun screen. Hats may blow off, assuredly will interfere with letting the wind blow through your hair, and cannot help protect you from the glare off the surface of the water and the boat itself. You will probably be out for hours, so choose one with a high SPF factor. For those skeptical of the true protection of sun screens, take a spray bottle of dilute vitamin C, take extra CoQ10 for a few days before and a few after your excursion, and have some natural coconut oil along.
Clothes are up to you, depending of course on the season, but also on what you are doing. Rafting down a canyon river does not call for shorts and tank tops, because the water feels like ice all year. Wet suits come in all sizes for those active souls, but for the rear cabin of a yacht, shorts will be just fine.
However, foul weather gear should be somewhere in your immediate vicinity, so provide it if you ate the boat owner or check on it beforehand if you are a guest. Open water comes with wind, and being out longer than you expect will make day wear inadequate after sundown. Squalls on the Bay and thunderstorms inland can drench you in a minute. This rainproof outer clothing comes in traditional bright yellow slick to fashionable color coordinates, and can be merely a shell or fully lined for cold weather protection.
For safety, you will want to have on hand a floating flashlight, a way to contact the shore or the folks that stayed on land, a first aid kit with band-aids (great for blisters, if for nothing more serious), lots of water for keeping hydrated, food because raw fish gets old fast, and polarized sunglasses. Sunlight is intensified on the water, so give your eyes the protection they need. Lip balm may also be very welcome after a while.
Of course, there are many other great ideas: gloves to keep the canoe paddle from wearing away the skin on your hands, a personal flotation device (no longer needs to be blaze orange and bulky, or always under your chin), a strap to keep your sunglasses or goggles firmly in place, a folding ladder to let you swim off the boat and get back in, and fishing gear to let you catch dinner. Towel, good books, radios for music and news, good friends – all of these can make things afloat easier and more pleasant.
Essential gear to bring on a boating trip is what personal taste and common sense tell you. You can also check out boating experts, from friends to the US Coast Guard, for advice.