I've got a laptop and have taken it with me on trips but the battery
won't last on a typical trip in the car.  

Would it be 'wiser' to buy a single purpose adapter that goes from
auto/plane to laptop ($80) or a general purpose inverter ($35) that
seems to push enough juice to power the laptop or something else if I
wasn't laptoping?

I've been leaning toward the single purpose device as I can see less
energy wastage going 12v dc to 17v dc rather than 12v dc to ac to 17v
dc, but at the same time I'd as soon not pound money down ratholes. 

Relatedly, any pointers on driving and typing at the same time?

TIA,

David