First aid supplies are essential to any prepper’s stocks. The majority of preppers I know have lots of guns, ammo, food and water but barely any medical supplies. It is essential that you know the basics of first aid so you can take care of yourself and your family should something happen. During an emergency, hospitals are generally flooded with patients in varying degrees of illness and injury. It could take hours before you see a doctor and in the case of a pandemic scenario, one of the most likely places to pick up the disease is, of course, the place where all the sick people are hanging out (but if you truly need medical attention, do not hesitate to get it!)
First, I always recommend that everyone take a first aid and CPR course. These courses are generally offered by the Red Cross and other various organizations for very little money and sometimes free. They usually last a day or two and are worth every penny.
Store bought first aid kits are a great start but I like to customize mine with products I’m familiar with using, as well as rounding out some things I find missing. What you put in your kit of course depends on your medical knowledge.
Next, every household should have a bare minimum first aid kit including the following:
thermal blanket (for treating shock)
triangle bandage (or large scrap of fabric)
maxi pads (can be used as a bandage)
needles and thread (fishing line or dental floss can be used in a pinch for stitches but please make sure your supplies are sterile)
basic medications (including ibuprofen, acetaminophen, anti-diarrheal, anti-nauseant, anti-emetic, etc)
This is just a basic idea of some of the things you should have around the house. Obviously, there is a lot more you can (and probably should) have but having the training to use these things can be a lot more important than the actual supplies. If you know how to treat the injuries, you can improvise the supplies.
I highly recommend having a First Aid manual on hand (paper copy), here’s an example of one I have at home: https://amzn.to/2xeieYT