Some amazingly unprepared people safely cross oceans in some pretty poorly equipped boats.
In my opinion, more important than safety gear is the knowledge and experience of the crew, and the seaworthiness of the boat.
Knowledge and experience requires that there is somebody capable of fixing things that break, or at least finding a way to make do without the broken gear. Seaworthiness requires that boat and gear be in well-maintained condition. Rigging is checked for weakness or damage before each and every offshore passage. Sails are in good repair, lines are in good condition.
IMO, the cleanliness of the boat is a fair indication of the care with which it is maintained. Dirty, greasy topsides - not good. Lines that are knotted rather than spliced, frayed, old and stiff - not good. Badly stowed gear lying around - potentially dangerous and an indication of sloppy thinking. For crossing any offshore passage I would be very distressed to see jerry jugs stowed on deck obstructing safe access to the forward deck. Other risks of this practice are even greater.
Knowledge and experience ensures that there is always somebody on deck to maintain a watch, and that person knows what they are looking for and looking at. Does that sound cryptic? We had a young fellow sailing with us in the Bahamas and he had no idea that a tug boat approaching us was too close and required avoidance measures, nor did he understand that we had the maneuverability to get out of their way, they did not have the maneuverability to get out of our way.
There's more to this, but I hope this is a start.
As far as "safety gear". Crossing the Pacific, I would recommend:
proper Personal Flotation Device (PFD, or also called a life jacket), and safety harness fitted to you. There are many nowadays, approved by the Coast Guard, that combine both the safety harness and the PFD.
Links to some examples: http://www.defender.com/product.jsp?path=-...36864&id=337716
And here's a link that defines the various "types" of PFDs: http://www.boatingsafety.com/boats/cgpfds.htm
A whistle on a lanyard to be worn by every person on deck. A personal strobe for each person to be worn. This would make it easier to be seen should you fall overboard.
The boat should have a 406 EPIRB. I personally think that it would be prudent and safer to have a High Frequency radio, either Marine SSB or Ham radio, and the knowledge to use it. Most passagemakers will stay in touch with other boats as they make their crossing, with a scheduled radio meeting once or twice a day. There are many accidents at sea that are non-fatal that, if help can be obtained, results in discomfort perhaps, but does not end in tragedy. Communications with other cruising or commercial vessels in the area would be preferable to relying upon distant search and rescue operations.
I hope that other cruisers on this board can contribute their ideas because on this I am very opinionated.
My final two cents (for a while, anyway): I don't believe that there is anything, anyone, anyplace, anywhere, that can ensure someone's safety. Although the overwhelming majority of boats setting out to cross oceans arrive safely, nasty things can happen. All you, or anyone, can do is to do their best to ensure that they are as well-prepared as possible and are on a boat as well-cared for as can be.
Cruising the South Pacific is an incredible adventure that you will remember fondly forever.