On an LtAP Mini, apart from:

* Disabling Wifi;
* Running the CPU at the lowest speed of 550MHz;

What else can be done to minimise current draw, indeed on any Mikrotik device?

You can maybe minimise the power draw (which is I suppose what you actually have in mind) by finding the optimum input voltage. To deliver the same power, you need the less current the more voltage you use; in ideal case, this would be an ideal hyperbolic function (I[Amp]=P[Watts]/V[Volts]), but the DC-DC converter inside the RB may have some optimal input voltage where the losses of the DC-DC conversion are minimal. Never tried this myself, but it should not be a big deal if you have a variable voltage source and tools to measure current and voltage.

You can maybe minimise the power draw

OK, some more information, the voltage is fixed at 12V so I really am looking to keep the current draw down. Potatoes potahtoes.

Apart from slower CPU and disabling unneeded packages and services I don't think I have many levers to pull on this one. I don't use the CAP LED, eth LED or WLAN LED so there is no advantage disabling them and the power and GPS LED are not controllable though useful to leave going in my case.