I'll agree with Gotak on this. When I knew I was going to be going to events and places where a telephoto would be useful, I brought along a lightweight crop body so I could switch instantly between the two at things like the Edinburgh Tattoo and in Oslo on the water touring the bays and islands.
Otherwise, rarely do you need more than something in the normal wide to low telephoto, like 24-105 for FF and 15-85 for crop bodies. If you are a birder, that's another story.
I just got back from a trip and had no problems carrying everything as carryon. A Domke messenger bag carried camera, two lenses (60D, 15-85mm and 70-300 DO) and monopod, plus all chargers and cards and cords and medications, using the Domke backpack strap. My roller V2 International Thinktank bag carried all clothing, laptop and some photo items (RRS monopod head), shoes, etc. and all my personal stuff was in a vest that I could take off and throw on a tray for search and destroy. But I cause the scanner to ding everytime, old surgical mesh in my abdomen, and I get thoroughly searched, including my bags.
Still it all went in the cabins through Delta, KLM and Air France.