Hi Don,
In the US we don't have weight limit for carry on, they don't weigh your bags.
http://www.delta.com/content/www/en_.../carry-on.html
For international flights the usual weight limit is 22 lbs, which is still enough for think tank + one long MK II super telephoto lens. The camera body and TC's + short lenses go in my backpack (you are allowed two pieces). I check the batteries, charger, flash, tripod etc.
when flying in small aircraft with small overhead bins such as Canada regional jets I use my light super telephoto lens, (400 DO MK II) which fits in a small back pack.
I have to actually catch a flight right now, have a nice holiday.
Best