This year I began experimenting with always leaving film cassettes in the plastic canisters to see if it would cut down on the scratches I get from dust getting onto the leader/felt. I'll admit that I didn't exactly take notes on the results, but my observations were that I got the same amount of scratches as before; which is to say, rarely and unpredictably.
For travel, I generally carry my film in a gallon-size freezer-thickness plastic zip bags. The most I have carried with the canisters is 40 (I do not have separate check-in luggage). For an upcoming trip I will need minimum 70 rolls (50 days of travel--and although my average at the end of a trip is always barely over one roll per day, I'm worried about being too conservative) and I am not sure yet what I'll do about canisters. If they don't fit, I probably won't bring them.
I've recently been working on a project where I shoot 3-5 rolls within a few hours, never removed from their canisters until use, only in one camera. Usually I have no scratches, but for a couple shoot days, one roll would have (minor) scratches while the rest wouldn't. I'm considering the possibility that some particle got on the film in the wash stage and scratched its way down the emulsion as the water dripped off..which would still mean the canisters didn't necessarily do much. While in the zipped plastic bag the cassettes and leaders do rub against each other, I do keep it zipped any time I'm not taking film in or out...I don't think too much dust is introduced. I don't tape the leaders down.
I know it doesn't seem like the canisters are much bigger than the cassettes but it depends on how you travel and what kind of luggage you have. I've found the difference to be significant, even though I went ahead and made space for them on the last couple trips.
Those egg-crate-esque Japan exposures film holders seem cool, but for the way I pack the film into my carryon, they're not practical...I need a more malleable mass of film, as un-structured as possible. But your packing style may be different.
Extra plastic bags are useful on any backpacking trip, whether you're a photographer or not. In my case, I take film from the main stash gallon bag and pop a few rolls into a quart-size bag that goes into my daybag once I get wherever I'm supposed to be. I also separate into multiple gallon bags when a trip has distinct parts so I know which is which when I get home...like last year when I had 4 days at a wedding in Belize and then went to El Salvador for 9 days alone. This time I have 10 days of a family trip to China/Taiwan which I will segue into a solo trip to Indonesia. I want two clearly marked separate bags of film...both to feel safe when I'm running down my mental checklist each time I'm packing up for a new place but also to know what to develop first when I get home .