The first thing one should do is get first aid training from a good source. If you've got equipment you should know how to use it!
Amen. Once you have training, the equipment list will come naturally, as you will want to have the gear that works with the interventions that you've been trained to perform.
Let me "third" this thought (since Chaos already seconded it). For a long time I was confused about what should go in the FAK or what my medical gear should be for emergency situations. It wasn't until I got some training that I realized I should just equip myself for the things I know how to do. A disaster is a really bad time to do attempt brain surgery with a Doug Ritter knife and an instructional manual if all you've done in your life is putting a bandaid on.
The same is true of many "prep" areas. Guns, for example. All the time people ask on the internet: "What's a good carry pistol?" "What's a good home defense shotgun"? "What rifle for SHTF?" If you need to ask, you probably should sign up for some classes. (Unfortunately, much of the time the people who respond to such inquiries also need to take classes themselves.)
Of course, from that perspective I am woefully underprepared in some areas. My bushcraft skills are basically non-existant. But it's surprisingly hard to find classes, and they're frequently expensive to take. The same is true of emergency medicine. There isn't much out there for us weekend warriors. But the biggest cost factor is the travel involved. If every city had a competent instructor in each of the areas we want to study, we can probably do it. If we have to take five days off from work to fly somewhere in order to learn a skill that we may never get to use, we may not be able to make that sacrifice.