This scene also illustrates the almost comical difference in each character's diligence. In an earlier breakfast scene, Ennis had the food cooked in perfect timing with Jack's arrival at camp. Here, Ennis has been at camp long enough to dismount, strip down a bit, and wash/shave his face — and Jack is just now opening the cans.
I think you're right in this illustrating the difference in their characters. But it could also be taken to show how relaxed they've become with one another. Or it could well be that this is hinting about how they (consciously or subconsciously) are finding ways to stay together more and for longer periods of time, even when appearing to just be attending strictly to business as usual. Perhaps Ennis rode down to camp super-early, knowing that Jack wouldn't have breakfast ready yet. Or Jack dawdled more than usual on purpose. And none of them complaining! At least not about that.
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All the
"J&E alone in camp" scenes have managed to imprint on my mind a strong and enduring impression that what we see is the truth of it; - that Jack and Ennis were really once all alone out there, on a mountain, far away from other people.
So though of course I *know* about the filmmaking process and all the crew and equipment it takes to make the smallest scene, still I feel a bit surprised when I see pics like the one below, from one of the other early scenes. Seeing images like that never fails to reinforce my admiration for the actors, admiration and wonder that they are able to stay in character, and to give us these two wonderful completely believable cowboys, with all that stuff and all those people hanging over their heads.