Invertors, connected on an as-needed basis to a vehicles wiring system, may meet the need for some.

Woot happens to have one such available today: a 3000 watt pure sine wave model that I am finding tempting: https://tools.woot.com/offers/gowise-3000w-sine-wave-power-inverter?ref=w_cnt_wp_2_2

It appears this model does not come with wiring cables: these would be a separate purchase.

Usually, models of this wattage are double the $180 price of this brand.

It's not enough juice to run a whole house AC or heat pump perhaps but probably enough to keep a fridge cold and keep the food from spoiling.

Even bigger invertors are available, up to 5000 watts.