What are some parameters for the long car ride? An 8 hour, straight through drive in a Miata vs. a 3 week jaunt in a class A RV allow for vastly sdifferent adaptations.
TripleA on a laptop is probably the most portable you could get without loosing to much fidelity.
Physically, printing out the maps in 8.5"x11" and slipping them in clear page protectors to make an atlas book and using dry erase markers to indicate units may be the most compact way to play G40 in an analog variant. Imagining those old choose-your-path novels - to invade Russia, turn to page 7. Could have different pages to mark income and even a battle board.