I've found that most first aid kits are lacking when it comes to any trauma more than a paper cut. I keep a cheap first aid kit for the paper cut, blister type incidents that's mostly bandaids and tape, it saves digging through my trauma bag every somebody nicks themselves. The trauma bag has stuff for more extensive injuries.
For major injuries gauze dressings and tape are your friends. I'm going by memory here but I have 10- 4x4 dressings, 10- abd pads (5x9 dressings) 1- trauma dressing (large not sure of size) 1- roll of 1'' and 3" tape the cloth type that actually sticks, 3 or 4- rolls of 4" cling (rolled gauze) 2- ace wraps, 1- SAM splint (malleable aluminum splint that can be shaped to do just about anything) 2- triangular bandages (in case you can find a boy scout that can do a sling and swathe, I've never been able to figure that one out), 1-vomit bag, Disposable gloves, remember if it's wet and sticky and not yours don't touch it. 2-each disposable self activating hot and cold packs. 1- trauma shears
I work as a Paramedic so I have advanced airway stuff but for the layperson I would add a pocket mask for CPR and a good first aid guide book.
I didn't buy a kit since I can get the stuff from work but I just bought a soft side tool bag to keep it in for a third of the money they sell the "medical bags" for. This place has some decent kits and also sell the stuff individually if you want to make your own http://online.boundtree.com/store/pr...SES%2C+STOCKED
If you know anybody that works for a ambulance or hospital they can probably order the stuff for you pretty cheap