I like the solar battery charger I saw on Bob's blog.
Many things can run on small batteries.
I did some comparison shopping after seeing the charger, and found there are an assortment of solar chargers. I can't remember which is which now, but there is a charger that can charge a laptop battery and more -- reaching 19volts and my laptop only needs 18. I'll have to shop and compare some more.
I'm staying away from propane right now. I have a small van and can break a frost with a candle heater. I won't be camping in a deep freeze if I can possibly help it, and I have done camping where I woke up with frost on my face -- but I survived it, thank you very much. Put coffee on and no hyperthermia to report. That was in a tent with a sleeping bag. I'll be in a van with a lot more insulation around me.
Air-conditioning?? Well, I'm going to find places where I can park under a shade tree. If that doesn't work well enough, I'll pull out my big blue tarp and make a tent over the van. That would double the shade of the screen house. Or maybe I'll find a big fire blanket to cover the car with to reflect the heat.
I've run across a free (one is broken) solar yard lantern post (had 3 lanterns) that seems to put out some nice light. I'll unscrew the top piece and set it on my car hood -- or hang from something. I'm going to be patient and keep a lookout for cheap accessories, or even a full solar setup -- maybe get a fridge -- but I can manage without it. Maybe I'll haul cold water from a mountain stream to keep the veggies cool and fresh. Freezer bags are so handy for water or veggies or ice.
I'm also going to design a cooler with extra insulation around it, maybe woold blankets... inside another box, maybe using a sheet of foam to construct it.