I'm doing a multi-city trip through Italy this summer. I don't want to use the standard luggage since we will be doing a lot or train transfers and walking (cobblestone). Does anyone know if a large hiker's backpack can be used as a carry-on? I'm nervous to check it because we have a very quick transfer and I'd rather have all my stuff with me than to chance it getting lost in Dusseldorf somewhere. I don't have a backpack yet but was looking at the Teton 1500 but that seems too big for Air Berlin's restrictions (55cmX40X20) so I am also looking for recommendations on a backpack. Thanks!