George Barr has posted a topic on travelling light with photo gear and the problem of which stuff to choose. Basic premise is that all the main gear will be going handheld on the aeroplane. Just like it should.
This is a problem I've faced a number of times, particularly when I took the bike to Mongolia. there I was restricting myself to lenses that could fit into the handlebar bag - 2 lenses no longer than 5". And I want focal length coverage. tough choices.
For me there are 2 main aspects of the travelling:
1. What range of shooting (thus gear) do I want/need for the trip
2. What soft of bag/carrying solution do I need.
To point 1.
Firstly, you only get photos with the gear in your hand, so trades-off need to be made. If the gear is too big, it won't go out.
For me I'm mostly doing landscape stuff, so want wider angles. When I'm with the bike I want longer focal lengths for sports stuff and some wildlife.
This means compact lenses, image stabilisation on the longer ones, best performance for the wider angles.
Personally I take my 17-40L and either the 28-135 Is or the 70-300IS DO. The first and last of thee are a great combo on the bike. The DO isn't the sharpest lens but stands up well to post-processing & sharpening and I'm generally not using it for stuff to print big anyway. Despite that
I've jut done a 25 image stitch that runs to 6' wide and has excellent detail as far as I'm concerned. Not quite fine-art standard, but good enough.
Those 2 (17-40, 70-300) fit nicely in the handlebar bag and mean I've always got the right lens with me. I also had the 50 f/1.8 and 28-135, the latter hardly got used. Its strength is when I want 1 walk-around lens.
I'm going to get the new EF-S 17-55IS as it'll be even better than the 17-40 as a walk around and for city visits. A 1 lens solution for a wide variety.
If I was doing finer quality work, I think a great 2-lens combo would be the 17-55 and the new 70-200L f/4 Is. Could even take the 1.4x telecon for little extra weight.
I'm working on a solution for the Shen Hao 4x5, but probably I'd take it and the 17-40 (or 17-55 when I get it) and be done.
To point 2.
Unless I ever go on a major shooting break with big, expensive lenses, I don't see the value in dedicated photo travel bags. If I'm carrying the bag with me, all the protection required is something to wrap the gear in.
I'm now using my small carry-on bag, which is max size under new regs.
I can carry the body (in its own pouch) and about 3 lenses, plus the chargers and portable hard-drive. On top of that I can carry enough clothes for a weekend, or a change and my laptop. If I was carrying the 4x5, then that and the 20D with a single lens would fit fine, together with a bunch of film.
The lenses go in separate bags. 2 small lenses (like the 17-40/70-300DO combo) fit into the bag for the 300L f/4IS and a soft pouch for others.
Chargers, portable disk etc have a small zip pouch that is quite flat.
All-in-all, much smaller than carrying a dedicated photo bag. If I need one of those, other gear goes in it and it goes in the suitcase/hold-all in the check-in. then I have it when I need it.
For back-packing I use a regular rucksack (slim, climbing style) and put the camera in a small pouch/soft bag inside. Light, small, easy to pack and get at. Again, I don't feel the need for all the padding if the pack is always in my hand. Tripod fits nicely on the outside compression straps, packed in a sleeping mat bag.
If something happened enough to damage the cameras, I'm pretty sure I'd have worse things to be worrying about at the time.
Other examples - when I did the Tour de France day on the Joux Plane, I had the 300 f/4, 1.4x and 28-135 plus a monopod. that with lunch and water fit nicely in the rucksack and was bike-able. Covered all the cycling action I was doing.
The biggest compromise I think that needs to be made is the trade-of between highest quality lenses and compact size. personally I'm happy with the mid-range or lower-L stuff. I don't do huge prints, so that's OK. Then I tailor the shots I take to the sizes I can reasonably print,
accepting that I can't get great shots of every opportunity I see but can for the most important subjects to me for that trip.
Were I a professional or selling my stuff, I think I might have one of the new Think-tank carry-on bags, but I'd still restrict myself to 2-3 lenses per trip, or a couple of outfits with a couple of lenses each.