There are lots of places that will sell you a first aid kit, some inexpensive with a few supplies, others quite elaborate, with price tags to match. None of it matters if you don't know how to use the supplies. I suggest, along with a good medical kit, you at least take a Red Cross First Aid course, or even go through a full blown EMT course. It could save your life or the life of a loved one.
Stock up as much as possible on medications you need to stay alive. Read up on alternative natural food and herb solutions that may reduce your need for commercial meds. See if a veterinarian has equivalent animal meds that may work in your situation.
DIY Medical Resources including "Where there is no Doctor"