First stop is to check who you are likely to fly with and their carry on luggage maximum size specifications. They do alter from airline to airline as indeed do the weight allowances too. I have three specifically designed camera bags, each one purchased as my lenses got bigger. Should have thought about what I was going to get in the future really and then I'd have less bags now! Think Tank make decent bags, they are pretty expensive but they do the job well and have aircraft travel in mind too.
One the other hand I have a 4th bag which I use for special occasions when I want to take my biggest lens. It is very lightweight, far lighter than any camera specific bag I own, but it's within size limits and will actually take a 600mm f4 lens at a push. There is no inside protection so I wrap the lens well in bubble wrap and I am careful not to trust all the weight on just one of the back straps. Bought it in Home Bargains store for £10 and with the lens in I can still travel when the carry on allowance is 5kgs in weight although of late not needed as Thomas Cook have increased theirs to 6 kilos.
Be careful though, the likes of Ryan Air who I haven't flown with but I am told do make frequent checks on size.