EVs don't have alternators. They have DC-DC (that's direct current to direct current) converters, which take pack voltage and reduce it, usually to about 12-14 volts. The Leaf's DC-DC converter can provide about 1500 watts for accessories when the car is parked. While driving I'm sure it's less, so you'd need either a mini fridge with modest power requirements or a deep cycle battery to act as a buffer and reserve power supply for the inverter. You could replace the Leaf's mediocre 12 volt, 20AH or so OEM starting battery with a much larger AGM battery, with the inverter wired to it via a fused cable. I would also strongly suggest a hardwired battery maintainer lead to keep the big accessory battery up to charge.
Scarlet Ember 2018 Leaf SL W/ Pro Pilot
2009 Vectrix VX-1 W/18 Leaf modules, & 3 EZIP E-bicycles.
BAFX OBDII Dongle
PLEASE don't PM me with Leaf questions. Just post in the topic that seems most appropriate.