I've done that exact thing, but my dad had quick reflexes and grabbed them before they sunk.

http://lmgtfy.com/?q=floating+sunglass+lanyard

Y'all need some common sense. Buy a 5$ lanyard or less expensive sunglasses. 

I use 50$ JP fitovers and I always use a lanyard. 

Man I wish I could stand contacts

Stuff happens... 

Sitting in a kayak, with my cell phone in a dry bag.  I had brought it because my mother's health has been a little off so I wanted to be able to get a call from her or my wife if needed.  Sure enough, phone rings and its mom. Talk for a few, everything's ok.  

By the time we're done, it's getting late and so I decide to make one more quick cast. Phone on my leg (why I didn't put it between my legs, I'll never know) until I accidentally brush my arm over it and slide it off my leg and over the side of the yak. 

The best part:  The phone has... er, had an environmental error condition.  If it was subjected to WAY to cold/hot/wet conditions, the LED flash for the camera and the alert LEDs on the front of the phone would flash. So, an instant after hitting the water, the lights started blinking... I watched as it slowly flashed into the depths only to flash no more.  It was a cool, eerie little light show.