I see a lot of occasional paddlers don't wear PFD's, probably because they aren't comfortable, particularly in warm weather. I sometimes take mine off in flat water to cool down, my thinking is that I can put it on if I go in the drink. It's hard to imagine a situation out in the bay where the dad couldn't get to his vest and put it on. I can't imagine the father didn't have a PFD in the boat, not being out on open water.

Average temps in LI Sound are in the 70's during August. Smithtown Bay would probably be warmer. This past summer was warm. I don't see hypothermia being an immediate threat. Most (all now?) yak's have flotation chambers or Styrofoam so they float when capsized. Why couldn't he hold on to the boat?

As for the sternum-strap whistles, a couple of my day packs have them. REI also sells them as an add-on to your existing pack or vest. I can't find it on their website, but saw them in my local store near the first aid supplies.