Healing kits are listed on pg 151 of the PHB/48 of BD&D (in the general equipment section, not the tools section) and it's text is as follows:
...The kit has 10 uses. As an Action, you can expend one use of this kit to stabilize a creature that has 0 hit points, without needing to make a Wisdom (medicine) check.
So yes, you could possibly use a Herbalism kit to gain proficiency on your medicine check if you don't otherwise have it (this would be up to your DM and available resources), or you can use a Healing Kit (And a use of said kit), to stabilize another creature.
There is also a feat that buffs this kit (The Healer feat)
Ultimately, what I think I would do, would be to allow proficiency with an Herbalism kit to allow for the creation of Healing Kits.
Does the Medicine skill have hidden uses you don't know about?
Doesn't every skill?
Remember that skills are abstractions of knowledge, expertise and ability. So in addition to the mechanical benefit (that of stabilizing a character when a healing kit isn't available), it also has other benefits.
Things that could require a medicine check:
- Diagnosing a wound in certain situations (can you move this guy who just fell off of a building, or will that harm him further?)
- Are these herbs useful for medicine/potion creation? (though this is the domain of the herbalism kit, it's probably a place of strong overlap)
- Diagnosing Disease, or even what poison has affected a character.
In addition to a number of other things.
This gets to a larger point about skills; yes, skill slots are valuable, and no you probably don't need Medicine as a skill, but as a party you probably want someone to have it, or at least someone like a bard who will get half proficiency in it.
Ultimately, skills like this one are going to come up way more in the exploration and social interaction phases of the game than in the combat phase. But that's ok, that's supposed to be 2/3 of the game, not a small part by any stretch.
Best Answer
Yes, you can make a Medicine check without any equipment
A healer's kit allows you to stabilise without making the skill check (PHB, p. 151):
Alternatively, page 178 of the PHB says about the Medicine skill:
One requires equipment (and has a matching cost) but removes the need to make the roll, while the other requires nothing special but has the chance of failure.