My wife is a degreed biologist, and works as a wildlife rehabilitator...think "vet tech" without the dog and cat orientation. She knows how to administer a variety of drugs (although not to humans) and probably has the wild animal equivalent of a paramedic's knowledge. Consequently, she is the designated "medical officer" aboard.
I will take St. John's Ambulance courses before we set off, and we will have a general first-aid book plus a "marine" first-aid book along, as well as an extensive medicine chest that includes splints, a BP cuff and an array of suture equipment.
Most boat injuries are of the impact and/or burn variety, with a lot of sprains and hand injuries included. We have already decided to forego boat insurance in favour of extended medical insurance, but we have yet to figure out whether flying "home" to keep our provincial health plan coverage active (the purchased insurance would extend this, not replace it) is cheaper than buying a whole "offshore" package, as would an American, for instance.