We do include whistles on our live jackets, and a couple by the doorway.
But, we each carry a waterproof hand held VHF radio, and a Personal Locator Beacon with us--either on the jacket or in the small ditch bag we carry.
The boat should have had floatation. 3 foot seas are very significant, early in the day--good chance that seas will increase.
The issue of an open transom, in on self bailing boat is a serious issue. The splash well in the C Dories have real virtues, but a self bailing hull is better. However, even a self bailing boat, when filled with a large wave is likely to capsize.
Agree so many mistakes--but even with mistakes, if life jackets, radios, EPRIBS are back ups which will save lives in the eventual danger.