There are a number of inverters available that produce about 70 Watts which will run and recharge a laptop on planes. Most carriers use the EmPower conncector.

1. Ample Power Corp produces the APC PnoteAC75.
2. Konnext 90-watt Universal Auto/Air adapter.
3. Targus has a couple of models as well.

All will be useable in planes and in cars.

The size and weight is comparable (1 lb).

The cost is comparable.