Whenever I am flying internationally I carry, inside my handluggage, a (n empty) black drawstring bag, which I whip out at the duty free shops and fill up with booze, etc. It's easier to carry (over the shoulder) than the duty free bags, & can be squeezed in anywhere.

TropicalFlyer - always pack the light things in the bag which goes into the overhead compartment, and put the heavier things at your feet. I once took a 15 kg roller on a series of connecting flights: I could barely lift it over my head... (the luggage allowance on that route was 20kg, and, being a student, I couldn't afford to pay excess baggage charges) It can be difficult to make an incredibly heavy piece of handluggage look as light as a feather when parading past a series of eagle-eyed airline staff...