TIL about car microwave pouches. It's a zipper-close foil pouch with a microwave emitter panel that runs on 12V. It has so few safety features compared to even the cheapest kitchen microwave!
At a max of 90W I suspect it's dang slow but the volume in the pouch is small so maybe it can warm (not cook) food without too much delay.
At ~$40 it might be worth a try but first I'll look for trustworthy reviews.
#vanLife