DG awareness is all that is needed for casa regs on charter
there is a reg I remember seeing somewhere for first aid on rpt min 1 first aid qualified crew to x number of pax type of thing flight attendants usually have a first aid ticket.
With some operators it could be a state/work cover requirement to have a first aider in each crew or could be a part of the safety management system or safe work method statement for some operators particularly those with mining or construction clients.