My jobsites usually have AC power so I just have a kettle handy in the car. Looks like this may be viable, has enough capacity for the Impress. I have bummed hot water from Starbucks and fast food restaurants, just get a fill from the tap on their Fetco. You can find all sorts of automotive accessories made for truckers at truck stops or online.

https://www.amazon.com/Uniox-Cigarette- ... B00H4OYITE

propane stove + https://www.heartroasters.com/products/tias-kettle ?

Aeropress with a Porlex hand grinder for sure. Pre-measure your beans ahead of time so you don't have to worry about that on site. Ready to go right into the grinder (at a medium setting) and dump into the Aeropress using the inverted method. Put a filter (or two) in the cap, pre wet the filter. Fill the water up to #2, turbulently swirl for 20 seconds, after that, fill water up to the very top. Put filter cap on. Place cup on top, flip over and press for 45 seconds. Once done, to dispose of coffee and filter, push it and a lovely puck of coffee will come out. Give it a quick rinse and the bottom seal a wipe and you're good! You can get the Aeropress that comes with a pouch and the Porlex fits right into the Aeropress so it really is convenient, easy to use and doesn't take up much room.
*Try not to use boiling water as it will burn the coffee and create bitterness

Enjoy!

We have a commercial Bunn coffee maker in the kitchen at work that dispenses 200f water from the hot water tap. I carry a Feldgrind in my work bag and keep a Clever Coffee Dripper at work for my single cups. I also keep a large Espro P3 at work for sharing with my co-workers.