Everyone’s medical needs vary — thus so do first-aid kits. Pharmacies, grocery stores, outfitters, and even auto parts stores sell pre-packaged first aid kits. It's not a bad idea to have one of these kits in your car. However we do not recommend buying one for a thru-hike, even those sold at outfitters. Instead we encourage you to create your own kit based on 2 considerations: your personal needs & the Appalachian environment.
When assembling your kit, consider your personal needs and then assume the worst case scenario will happen. If you have asthma, suffer severe allergic reactions to insect stings, wear contacts, et cetera, and then assume you will have an asthma attack, be stung by bees, or get an eye infection. Everything you'll need in that circumstance (inhaler, EpiPen, glasses) should be in your kit.
Finally, a note about short hikes vs. long hikes. Your hike's length does not alter what goes into your first aid kit. What goes into a kit for a 2-3 month thru-hike is exactly what goes into a kit for a 6 month thru-hike, or a 3-day weekend trip for that matter.
Balms, Ointments, Drops
Does it do Double Duty?
As with other gear, you want things in your first aid kit to do double duty whenever possible. This saves weight and reduces the size of the kit. A few examples:
Snake Bite Kits
We strongly discourage you from including a snake bite kit or suction products like the Sawyer Extractor Pump, as part of your first aid kit. Our article about venomous snakes discusses the issue in more detail, but in summary, the medical consensus on snake bite treatment has changed tremendously in recent years. Snake bite kits contain scalpels, tourniquets, and suction devices in order to perform the "cut and suck" method. Once widely taught to Scouts, hunters, hikers, et cetera, the cut-and-suck is now understood to do a great deal of harm for zero benefit.