Easy homebrew rule off top of my head would be a #of uses. Say Basic civilian medkit is 1-5 whereas combat medkit is 15..or same for large prepper style backpack size medkit. Damage of wound is # of uses needed. Only the combat and doc kits have the drugs for nerve/blister agent gas treating.
In looking online...i found a triage/flowcart that GMs might want to take a look at for giving medics a bit more description on what they need to do/are doing:
https://emsa.ca.gov/wp-content/uploads/ ... e_2017.pdf
And this link gets into some details of all the issues going into emergency care.
https://www.airmedandrescue.com/latest/ ... hot-wounds
I think it is safe to say that the one use per kit is a simple mechanic to prevent the game getting bogged down in the myraid of tools/supplies needed for the variety of wounds.
You can see the variety of items carried in the different kits. So does the kit have enough materials/tools? Your car roadside emergency/home kit is meant to help a knee scape...not a sucking chest wound.
It would be nice to have a bit more detailed medic/doc/emergency responder and remedies found in nature sort of module/supplement for those that want to have a richer medical part of the game.
Is there one from another system? I cant think of one offhand.