There is no “Healing Kit +1”
There is the “Healer’s Kit” which gives a flat +2 circumstance bonus on Heal checks. You can’t get it in +1 format that I know of.
Heal Skill: Long-term Care
In any event, the Heal skill in 3.5 doesn’t really heal HP anyway. There is “long-term care” which doubles the natural healing rate of 1 HP/level/(8 hours), but that’s extremely slow.
Stabilize
The Heal skill can, at least, stabilize a character so they don’t bleed out. That only takes a standard action. Getting him out of there now that he’s stable is going to be a problem.
Pathfinder: Treat Deadly Wounds
Pathfinder adds the “treat deadly wounds” option to the Heal skill. This heals the same amount as long-term care, but it takes 1 hour rather than 8. If you beat the DC by 5 or more, you get to add your Wisdom modifier to that, which speeds things up dramatically. It also requires two uses from the Healer’s Kit.
Dandwiki.com homebrew
The healing kit is what is known as “homebrew” – fan-made additions to the game. They can be quite good at times, but dandwiki.com is notorious for A. not visibly marking homebrew from homebrew (and, at times, simply mislabeling things), and B. having absolutely no quality control, so a lot of the homebrew is very bad.
This isn’t awful – the idea of having the Heal skill actually heal HP is a good one. As it is officially, Heal is nearly useless past like level 1. However, a number of its features are poorly chosen: it does not state how long the healing takes, and healing 1d20+(bonus to Heal skill) is enormous when you consider that actual magic heals quite a bit less than that. Also, apparently, each kit is one-time-use, which is weird.
Anyway, I cannot actually tell you if you can use this item in combat: it doesn’t actually say. The line about taking 20 (“When not threatened, a person may take 20 on a Heal check with a healing kit.”) implies that it does work in combat, but I have no idea how long it’s supposed to take. I think you can probably find material a little better than this, if you want a homebrew way for Heal to actually heal HP.
Conclusion: Get some magical healing
The Heal skill heals HP pretty slowly. The treat deadly wounds option in Pathfinder is massively better, but it’s still your level plus their Wisdom bonus per hour. That’s really slow. Magic is really the best way to heal, and the only way to heal in-combat, or even between combats if you’re in dangerous territory.
This advice may not help you right now, but in general, you guys need to find some magical healing.
You don’t need much, just enough to top you off between fights. A wand of cure light wounds does wonders; if you’re using 3.5’s Spell Compendium, a wand of lesser vigor can be even better. Anyone with even a single level in bard, cleric, druid, or ranger can use the wand of cure light wounds without using Use Magic Device; the druid and ranger also can use the wand of lesser vigor.
Alternatively, if you have no one in any of those classes, using a wand is a flat DC 20 on Use Magic Device anyway, which means anyone with a decent Charisma and some time to kill can just keep trying until they get it (unless they roll a nat-1 before they roll enough to hit 20). A few ranks in Use Magic Device can make this a pretty easy check; the skill is highly recommended.
Wands of CL 1, 1st-level spells (like both cure light wounds and lesser vigor are) cost 750 gp for 50 charges. That is too expensive for 1st level characters, but after you’ve earned some gold the group should pool money together for one.
If 3.5’s Magic Item Compendium is in play, there’s also the Healing Belt, which also costs 750 gp. These can be used by anyone, which is useful, and great in emergencies. They also recharge daily, which can make them a nice investment (though by the time you go through 50 charges of cure light wounds or lesser vigor, another 750 gp will be small change to your group).
Side Note: Combat Healing is overrated
In almost all cases, in-combat healing is wasteful; that same character could prevent more damage than he could heal by simply having the enemy die faster. The only real exceptions are emergencies (you don’t let your ally bleed out), high-level healing spells (namely heal and mass heal), or cases where you can heal while doing something else (e.g. several maneuvers from the Devoted Spirit school). Aside from those cases, though, healing just doesn’t keep up. The cure spells, in particular, are very weak, especially the higher-level ones. Save the healing for after the fighting’s over.
Best Answer
You basically... can’t.
The abstraction that is hp is nebulous and fluid; it’s not an abstraction for any one thing, it’s not even an abstraction for the same thing at a given time. If someone loses hp because a goblin slashes them with a sword, and then someone uses martial spirit to inspire them to greatness, they are healed a certain amount of hp. Here, hp was lost due to injury (probably?) but the damage healed was more inspirational in nature.
The best single thing we can call hp is probably “plot armor,” because that is effectively what it is. That is both its narrative and its mechanical role. Characters have hp because our plots and narratives want them to withstand more punishment than anyone realistically could. Characters survive blows—losing only hp, but otherwise being uninhibited by any injury—because we want to see more of them. And plot armor is always a matter of hand-waving. Good authors can make it more subtle and hide it, but it’s still there because of the demands of the plot.
In short, plot armor is not an effect, it is a cause. The narrative warps to reflect its needs, rather than it reflecting the events of the narratives events. And hp is basically a measure of plot armor—which makes it a little more reflective of narrative events, but only so much.
Finally, stuff like broken bones and sprained ankles—even the lost limbs mentioned by regenerate et al.—just... don’t factor into the system at all. No amount of lost hp causes those things, and those things aren’t defined as costing a certain amount of hp. In fact, those things aren’t defined at all. No effect in the game, anywhere, causes such injuries. As far as the game is concerned, therefore, they cannot happen, and it isn’t the rules’ responsibility to explain how to handle it if a DM decides to houserule things to add them. Instead, that DM is left on their own to handle it, and most DMs simply... don’t bother. Such injuries are either not part of the game at all, or they are matters of pure fiat that the DM is using, effectively, to railroad the players at particular points. You see that kind of thing in video games too—characters that have taken and dealt literally hundreds of attacks suddenly become injured by the plot, and no amount of your usual healing options help—you are forced by the plot to do whatever it is that the plot demands at that point.
A really fleshed out injury system could avoid all of those problems, but D&D 3.5e doesn’t provide one. It is a system that wants to focus on heroic epics—it doesn’t want anyone sidelined by injury, it doesn’t want to focus on the logistical hurdles such an injury causes, it wants to get on with the next adventure.