A doctor or medical professional and a small clinic for limited assessment and stabilisation. Not a hospital. Advanced imaging, surgery, intensive care, specialist treatment, blood banks and rapid evacuation may all be unavailable. South Georgia has no visitor medical service and no independent search and rescue, and evacuation from there can take days. The Falklands have local medical services, but complex cases can still need aero-medical evacuation.
Having a doctor aboard is genuinely reassuring for the routine things, and seasickness during the crossing is the most common one by a wide margin. It is not the same as travelling near a hospital, and it's worth going in with that clear.
That gap is exactly why operators require evacuation insurance and why South Georgia builds it into the entry permit.
Practical consequence for anyone on regular medication: bring enough for the whole trip plus delays, keep essential doses in your carry-on in original labelled packaging with a prescription list or doctor's letter, and check the rules of every gateway country for controlled or injectable medication. The clinic will not stock your prescription.