IMO and pretty much what I do, is keep a bunch of gang boxes. Kind of modular response kits. Some stuff is always with me, maps, compass, commo, cell phone etc., basic recovery stuff and first response, like two fire extinguishers, two first aid kits, flares. a magnetic revolving light (or strobe light), hand held spot light and two flash lights. I'm a firm believer in redundancy. Folding shovel, crow bar, gloves, two emergency blankets, a body bag and other basic tools (a larger than normal set of cable cutters comes in handy).
I keep a small open trailer and enough pioneer tools for about five people, shovels, picks, axes, pry bars (all the way up to the five foot model), two chain saws (extra fuel and spares), a ten amp diesel generator and an extra can of fuel. A big angle grinder and a small angle grinder (Master keys for gates), cutting torch, five hundred watt work lights and other useful stuff. Nothing over about 80 Lbs. A whole collection of ropes, harness and cables.
The gang boxes (3 feet by two by two) make for a neat grab and run response.
I'm a game manager and most of my first response stuff, is grass fires and leading the Fire guys down the right road. Occasionally, I'm the first to spot a set of tire marks leading into the woods from the highway (at three in the morning). Most of my first response for this, is Calling for help and giving precise and accurate directions. Cutting the battery cable (if possible). Not much else I can do, except assess the injuries (do they need a doctor now or a chopper) and try to control the bleeding. I've always been told to leave them where they are, unless they are in immediate danger. If you have to move somebody, a six handled body bag works well. Two poles and it's a stretcher and folds up smaller than a jacket.
There is nothing worse than calling for help and not being able to explain where you are. Second worse thing, is using up one fire extinguisher and needing a second.
I repeat, the best first response is giving the alarm (communications), knowing exactly where you are (good maps) and situational awareness (don't become part of the problem, instead of part of the solution).