I keep a Firefly 3 attached to every life jacket. http://www.westmarine.com/webapp/wcs/stores/servlet/producte/10001/-1/10001/151463/377%20710%201214/0/Lights,%20Strobes%20/Primary%20Search/mode%20matchallpartial/20/0?N=377%20710%201214&Ne=0&Ntt=Lights,%20Strobes%20&Ntx=mode%20matchallpartial&page=CategoryDisplayLevel1&isLTokenURL=true&storeNum=8&subdeptNum=50&classNum=51

With lithium batteries, which are good for ten years, the units will be there and operational if we ever need them. I have an older model that is more than 6 years old. It works fine. I test them a couple of times a season and replace the batteries every three to four years.

I also carry a flashlight (usually a Surefire A2) on a lanyard, but I would think trying to signal with it would get tiring. It is more of a backup, and useful on the boat for low light tasks.

On a couple of life jackets I also have a pouch with two orange flares, a mirror a cheapie survival knife, and a whistle.

The rule on my boat is that lifejackets are optional for adults (mandator for the kids) until the wind hits 25 knots or the seas four feet. Then its mandatory.

All this and I rarely go more than a mile off shore. I guess I have been reading this site too long.