If you really want to think of what will be clinically significant in terms of the biggest impact of saving a life then I'd say the following:
- Arrest arterial haemorrhage (CAT or equivalent)
- Defibrillation of VF and pulseless VT, and cardioversion of VT
- Open and maintain an airway (OPA, NPA and LMA or equivalent)
- Remove foreign airway body (laryngoscopy and forceps)
- Ventilate and oxygenate (oxygen and a bagmask)
- Obtain a 12 lead ECG to identify STEMI and enable shortest possible time for direct to cardiac cath lab
- Use the FAST test to identify possible stroke and enable shortest possible time to thrombolysis if ischaemia stroke
- Bind a fractured pelvis
- A small number of medicines, specifically:
1. IM adrenaline in anaphylaxis and severe asthma,
2. IM ceftriaxone for meningococcal septicaemia or septic shock.
3. IM and IN midazolam for status epilepticus,
4. IM and IN naloxone for opiate poisoning
5. IM glucagon for hypoglycaemia
All of the above can be performed our EMTs (except laryngoscopy, naloxone and midazolam) and First Responders (except laryngoscopy, LMA, 12 lead ECG, midazolam, naloxone and arguably cardioversion but if they put the pads on and analysed and the VT was fast enough it'd cardiovert).