Rucksacks invite praise for their obvious practicality, leaving your hands free and distributing weight evenly across your shoulders instead of ruining your posture by weighing you down on one side. The bus-sized types also incite loathing, of course, leaving whacked-into passers-by in their wake. But these are the small ones (21- to 24-litre volume) - sleek, neat alternatives to cabin baggage that you can insouciantly sling over your shoulder or put on your back for an afternoon's hike.