i use a lowepro back pac thingy. not sure of the model# (since it is not labelled and I want to buy an slightly bigger one so I am a bit pissed at the moment, that will pass after several more beers...) but i carry 2 strobes, batteries, charger, wide angle lens, 3 p&s cameras & bodies and a bunch of (clean) underwear. All in a very small compact size much much smaller than the standard legal carry on size. It is only 6 inched high.
I think the breaking point is DSLR housing vs P&S housing.
I suggest you check both the "maximum" allowed carry on size limits as well as the "commuter plane" storage bin sizes. You can carry it on, but it will not fit in the plane. Sky check is your friend! Maybe?
My lowepro fits the commuter bins but is only about 6 inches high which is much much smaller than the commercial carry-on limit. I get to stow my stuff on every plane, while lots of people have to "sky-check" their fragile valuables.
Check the plane types you may be flying in. The "industry" has a standard carry on size (9x15.5x21.5in according to Air Canuk) but the overhead bins in many small commuter planes are much smaller.