The Exploration Medical Capability team (ExMC) at NASA-JSC is one of the groups tasked with scoping this very issue for us, and it's an ongoing project - there is currently no consensus on what the final outlay of medical capability for a Mars mission will look like.
For the International Space Station, we do have an agreed-upon list of medical capabilities (including medications and hardware) which has been honed by the medical operations group including Flight Surgeons and Biomedical Engineers over the past 20 years to cover the range of our most high-likelihood and high-risk medical needs. I don't believe the full list of our medical kits has been released publicly so I can't link you to that, but I'll tell you that what we choose to fly is greatly informed by our preventive medicine approach to risk mitigation on the ground:
We have a high degree of insight into the medical risk our astronauts are exposed to or carry with them, and we spend the years prior to their mission mitigating things like cardiovascular risk to the greatest extent possible. We also screen out any pathology that could pose significant risk progression during a 6 month or 1 year ISS mission. The result is that risk for most terrestrial medical concerns are well addressed prior to flight, and the risk of occurrence during a 1 years mission is quite low. Furthermore infectious disease are non-existent on ISS since astronauts are effectively quarantined for 2 weeks prior to launch (though there have been breaks in quarantine with resulting viral transmission to ISS, thankfully few). Musculoskeletal injuries do occur on orbit and may require intervention.
Finally, there are a range of worst-case contingencies such as cabin fire, emergency depress, or decompression illness during EVA that could occur, and we have the ability to respond to a range of injury presentations that would accompany those contingencies. The "big 4" of Fire, Depress, Toxic Atmosphere, or Radiation Event will be common to any long-duration mission, with the radiation event risk higher for any mission outside of the Earth's magnetosphere. Any future medical provisioning will provide some level of ability to respond to the Big 4 as a start. The question of pharmacological stability in microgravity/radiation environment long-term (where resupply is unavailable, unlike ISS), and of any changes in patient pharmacokinetics in microgravity (still largely an unknown) will also inform which pharmaceutical agents we can send for any multi-year missions.
The need to have a physician as a necessary part of any crew complement for an exploration class mission is well recognized. Giving them the tools they need to manage crew health without the use of real-time communication is an ongoing area of work. Even the type of medical background the physician astronaut should have is still a point of discussion (Emergency Medicine? Internal Medicine? Aerospace Medicine? Any surgery experience? And so on). I'd argue you want to send no fewer than 2 physicians, since your medical officer may become the patient.
It should begin to be clear why a return to the Moon makes infinitely more sense from a logistical planning POV on the medical side. It's a natural extension of our current concept of operations for ISS, whereas a Mars or similar exploration class mission profile would be a large departure from the way we've provided medical support for crewed spaceflight for the last half-century.