First don't have equipment/ supplies that you are not properly traned to use. Building you own kit is so much better than buying one already built. If you make your own kit you know what's in it an you can also build it to fit your needs. But here are some basics needs.
1) hemorage controll
-- like battle pressure dressings, quick clot, galls pads (4x4 and 2x2), galls sponges, and galls rolls. Also I have an ace bandage in mine in case more pressure is needed. And a must have is the female hygene Maxie pads, for wounds that are bleeding a lot they are better than the galls.
-- let me say it again only have medication you are trained and know how to use.
Good meds to carry are Tylenol, Ibiprofen, Benadryl and a antiemetic of some sort like zofran to prevent nausea. Also some eye drops, burn cream and antibiotic cream. And bug spray. I have a lot more meds in my kit, like antacid meds, eppi pen and more
----- if it is a SHTF situation then any antibiotic medication how ever not all antibiotic med treat every thing.
3) if you bag is big enough then splints and a couple of ace raps along with ice packs and some hand warmers.
4) air way supplies if you are trained to use them
--- band aids, alcohol pads, iodine swabs, non suture closing methods (steri strips, liquid bandages)
In my little kit I have all above plus sutures,needle drivers and wound care kit, nasal trumpet, OPA, and IV start kit.
I have all that in my little kit. It is the condor rip-a-way med pouch. It dose look small in the pic on line but it is the smallest-biggest kits I have ever used. I highly recommend it to anyone who wants a small bag but wants to carry a lot of equipment.
Also sorry about any misspelled words i am sleep deprive using my iPhone at work.
Here is the link