Basic First Aid and the Like
Most of these supplies can be found at your local drugstore but many times it's easier to order online and shop in bulk for a cheaper price.
There is a quick list of supplies on Amazon that covers all the basics from sterilizing packets to scalpels and sutures
Allegro Medical has a great selection of medical equipment from needles to scalpels to bandages and more. Can be a bit pricey for some things but they carry most brands and sell in reasonable bulk.