Alright, here's a new one: just carry liquid espresso shots. Before I leave for a trip I pull about three shots per day, bottle immediately and chill. Bottling them immediately catches all the aromatics and chilling just helps preserve the flavor. Then just heat up some water just above drinking temperature and mix in three shots, instant Americano. This year I'm gong to try individually packing days in squeeze pouches. If you don't have an espresso machine you can just swing by your favorite coffee shop and ask them to pull the number of shots you need, if you explain what you're doing they'll be relatively inexpensive.
Someone mentioned to "not boil" the water because it ruins the coffee, and it is true if you get the water too hot it'll taste bitter (too cold tastes sour) but above about 6000 feet you can't actually get the water too hot because the boiling temp drops.