The 'personal item' gestapo, especially since they now can start charging you for bags checked so there's a monetary incentive to them to be stricter, seems to me to be pretty rough on anything that doesn't look laptop-bag or purselike. That said, there's an awful lot of huge freaking laptop bags I've seen larger than the carryon I use for overnight clothing. 
You might get away with more of a 'holster' type DSLR bag that holds the body and one lens as a personal item...something more like THIS. I've got an earlier generation of this and I have taken it as my 'only' camera bag with a carryon full of clothes for non-UW trips (wasn't bringing add'l body, lenses, etc, just wanted the camera with me 'just in case' an opportunity to go walkabout presented itself on business trips and the like).
I don't see a need for a separate camera case in general, unless you think you'll be carrying a lot of wet or salty stuff home and don't want the camera exposed to that (and even then - would just toss some big ziplocks into my bag to do the separation). My carryon is a Lowepro Vertex 300AW backpack, plenty big for 2 camera bodies (below pro size), housing, strobes and arms, chargers, etc. sans the handle/tray assembly and the big 8" dome, which have to be checked with the scuba gear. Haven't had a problem yet, although the 300 is "at the limit" for airline travel size (US, probably over in Europe - didn't see your location in a profile) and definitely over it if I pack a laptop into the sleeve as well. So the laptop becomes my personal item in a courier-type sling bag.
