Yeah shouldn't be a big deal... while working at YVR, I had more experiences dealing with international departures and their security restrictions, but as far as I remember for the U.S side, it wasn't much different, and was never a issue.
I would imagine bringing the DSLR bag is no different than bringing a separate laptop bag, so shouldn't be a problem
By the way, you won't be able to put water in the DSLR bag before going through security anyways... and the only food they'll allow are the ones you get at the YVR food court
