I don't airsoft much anymore, but I've always gone out with a first aid kit I built myself based upon training received in the Boy Scouts and a college course in first aid, CPR and basic lifesaving. I built two kits, one that fits in a 200 round SAW pouch consisting of assorted bandages, alcohol swabs, rolled gauze, medical tape, ACE bandage with safety pins, 2x triangular bandages with safety pins (similar to military field dressings), tweezers, scissors, multiple pairs of nitrile gloves, tube of triple antibiotic cream, burn cream, small bottle of calamine lotion, chapstick, ibuprofin, antihistamine tablets, antacids, pepto bismol tablets, two cold packs and first aid manual. The smaller kit is built into a 100 round SAW pouch and omits only the largest items.
This was seen as the sufficient and proper IFAK when I was in the Scouts, but now it seems if you don't have any trauma gear, splints, airway barrier device, and quickclot, it's not a first aid kit. The way I was trained, if you weren't trained for performing a certain procedure or in the use of a certain device, you have no business having it because you will cause more harm than good. I still need to get a barrier device, SAM splint, eye dressing, small water syringe/pipet for wound irrigation, and a forehead thermometer. However, though I'm trained to perform an intubation and tracheotomy, I don't bring equipment to do it because it's been a long time since I received said training and I risk doing more harm to the victim than help.
While doing my undergraduate geology work at a university, I went on a number of multi-day field outings and a one month field camp, and I was horrified I was usually the only one who ever took an IFAK with them into the field, despite encountering injuries or minor emergencies where my kit was needed. Worst real life events so far have been extracting a glass shiv from my own calf, cactus spines from a friend's foot, repositioning my own dislocated ankle from a good fall, and having to patch up my own hand where I took out a dime-sized chunk of skin and meat out catching myself on a rock face in said fall. It's good that in the last 14 years I've had the kit (and been rotating stock to keep it current) I've rarely had to use it, but it sucks I've been the only one who really got injured enough to need it.