I agree on customizing your kit for your needs, a couple of young healthy people requirements would be different than a diabetic, or kids, or old.
Would also add a "stop the bleed" course to the CRP-first aid course. It is widely available these days (unfortunately), it is mainly directed to gun shot wounds but the same practices could be applied to any deep cuts or punctures.
I keep basic stuff when diving close to shore but going farther to blue waters or crossing to Bahamas is better to have more than less.
On the lines of blankets and fresh water I also like to keep some food set aside for emergencies, nothing special just separate from whatever we are planning to eat or drink. I used to focus on what to have for a person getting hurt but along the years I learned that is also good to plan for the non-injured person, the one providing the aid. Potentially this person has to also operate the boat back home after or during taking care of someone else's injures.
Depending on the style of the boat things can stay on board or have a designated bag/case to bring along on each trip.