if there was a problem w/FC on the laptop booting from the external will run the program.. if the OS on the laptop is messed up then you could not run the FC app.. so, for emergencies I would load the OS to the external drive too.. I have booted Tiger in the past from an external thru firewire (don’t think it would boot by USB..) also, I think it must be the same source disc as the macbook, something about root level protection that won’t let you open your OS from a different mac? I’m pretty hazy on that.. If I were going on an extended trip I’d want all the redundancy I could get.
Moto Guzzi rider
dog lover w/wife, Ex & 3 kids