A good first aid kit in the camper and the boat. Was EMT 1 for a few years. My CPR cert is expired and I want to try to renew it, but I honestly do not know if my back would hold up working on a full size adult, doing one rescuer CPR.
While working, I was 1 for 3 on CPR.
I also carry a handheld low-buck basic GPS in the boat and the camper. When on a lake, river or otherwise out in the hinterland, it is a helluva lot easier to guide in a rescue aircraft with coordinates than it is by trying to use landmarks or best-guess distances. If somebody really needs to be medivac'd, time is critical & gettin' the bird in quick can make a difference.