The skipper should make sure that there’s a proper first aid kit aboard, suitable for the boat’s area of operation and how far the boat will be from medical assistance. Being the medical officer doesn’t mean that the skipper must perform first aid if there is someone aboard who has more training in what’s needed. A trained person is the first choice for assistance.
The captain is there to make sure that what needs to be done, gets done. This may mean coordinating assistance on the VHF radio, assigning crew tasks for a medical emergency, and other responsibilities. Think about what you would do in the case of a disabling injury or illness to one of your crew or yourself, if you’re the skipper. If you normally operate with only one other person aboard, it’s essential for both of you to have a plan. Everyone who’s in charge of a boat should take a basic first aid/CPR course; the more trained people out there on the water, the better for all of us.