When it comes to medical kits, we've always believed its better to piece together your own instead of buying a premade kit. But of course there's always the exception that proves the rule, and that exception is Adventure Medical Kits. There are three major reasons for this: AMK makes a metric crap-ton of kits tailored to just about every possible scenario, they use high-quality components, and they don't extort a ridiculous premium for pulling it all together into a very nice package. At the very least, if this is your first medical kit rodeo you can start with an AMK package and build it into whatever your heart desires.
For 80 percent of us, one of their Ultralight & Watertight series of medical kits will do the trick. From the pocket-sized personal .3 to the hardback novel sized small group (1-4 people for 1-4 days) .9, the U&W kits contain a complete assortment of treatments for blisters, burns, scrapes, fractures, sprains and STDs. Wait, not the STDs, you're on your own there, and shame on you for not using protection! Paging Dr. Penicillin.
We like the .9 because it's really not all that much bigger and includes some important extras like diamode (for diarrhea), a trauma pad and extra wound closure (butterfly) strips. A lot of the stuff is double-bagged to extend shelf life and provide additional waterproofing should the waterproof bag itself be compromised. The next step up would be to add dental wax, a splint, tourniquet, chest seal and QuickClot. If you know you need these things AMK has a wide range of trauma kits too because of course they do, or if your needs are very specific you can read up and piece together your own. If you get to that point you should really consider getting some advanced training if you don't already have it, something like the 16 to 20 hour Wilderness First Aid course offered by NOLS.
Other things to think about are survival items like basic repair supplies, water purification tablets, fire starting materials, signal and lighting tools and a knife. Oh wait, AMK has you covered there as well with a slew of kits for urban and wilderness survival. You do have one in your car, right, along with an emergency jump starter and related useful items? The AMK Pocket Pak Plus is a bit spendy, but you get everything you'll need in a pinch including a tiny but nifty Doug Ritter RSK MK5 survival knife, worth at least $20 all by itself. All in all, if you've been putting off taking responsibility for taking care of yourself in the backcountry, your excuses have run out. Start with AMK and you'll never look back.