He who lets the sea lull him into a sense of security is in very grave danger. — Hammond Ines
Things can happen, even on a calm ocean, so it is necessary to be alert and to not underestimate the water's strength and unpredictability. Never be complacent, and don't trust the sea. Wear a life jacket (with sailing harness) and tether (especially when night sailing). Safety gear with auto-inflating systems need to be inspected often, and you must carry spares.
Safety gear will last you many years if serviced regularly. Pyrotechnic signaling devices (including aerial flares and hand held signals) expire 42 months after the date of manufacture in accordance with the Coast Guard requirements. Typically, this means that you must replace your flares every three boating seasons. Aerial flares cost $75 per pack of 6 (in Canada), for a boat our size (10 m) we need to have 12 aboard.
Life jackets and life rafts need to be serviced every 3 years, as the auto-inflating canisters need testing, and replacing. Replacement cartridges for auto-inflating PFDs cost about $35 (again, in Canada). If planning to travel for many years out of the country, carry replacement cartridges onboard, because other countries may not carry the ones required by your model and that replacements can't be shipped by air (they're pressurized). Re-packing a liferaft is very expensive, and varies depending on the model, and your location in the world.
Life jackets that are not auto-inflating are fine, but must have a sailing harness to which you can clip a short tether. If the tether is short enough, you won't fall overboard and won't require extra flotation. Floating life jackets that are non-inflating are bulky, and may make it difficult, or uncomfortable to sail in. Wearing a short tether that keeps you to the boat, and prevents you from falling too far overboard is your best security. We recommend a short tether with two clips, so you can clip to another point on the boat while always being clipped on elsewhere.
Run jacklines along the deck, from bow to stern cleats, and keep them within the standing rigging. Make sure the jacklines are flat, and brightly colorful so as to be visible at night. Rope jacklines can trip you up. An even better option for jacklines, is to keep them running as close to the center of the boat as possible, so that there is no chance of falling overboard when attached. Jacklines have to be made from a strong, UV resistant material, you can buy them, but we had ours made.
Every boat should have a ditch bag, that is, a bag filled with emergency supplies in case the boat needs to be abandoned. The bag should have a handheld vhf, spare batteries, noise-producing device, flashlight, water, food (energy dense), charts, sextant, ibuprofen, sunscreen, lighter, medical kit, fish line, fish hooks, mirror, compass, duct tape, flare gun, emergency blanket, etc.