I think there's some confusion here. I realize the scene appears in the film before the reunion, but what I am suggesting is that it was shot with the intention of being after the reunion, when Jack and Ennis were getting together on a somewhat regular basis. There is no scene withJack and Ennis in the truck in the movie. It is one of the scenes that did not make it into the film. It's shown many times on this forum in various threads, but did not appear in the film. What someone suggested was that the grocery scene was meant to go with the truck scene, but, for some reason, Ang cut the truck scene, then placed this scene where it finally is. I realize this is conjecture, but it is possible and puts a different spin on the scene -- one that I think is more probable. I see no other real reason for this scene. i do not think Ennis was that devoted to his job. It was only a way to keep bread on the table. He certainly din't mind leaving the job to run off with Jack when the opportunity came along. Just MHO.
Yes, that's an interesting idea, lamusica.

Had never heard that before, about Ang having moved scenes into a place different than originally planned. Do you know if that tidbit came from an interview or was it speculation? I find the whole filming process fascinating, it's always intriguing to hear what actually goes on in the minds of the people putting a film together.
Have to say though ... I still have trouble thinking that the grocery scene was meant to take place at any point except during the four years that Jack and Ennis hadn't seen each other, before the first postcard, for a number of reasons.

The scene just seems logical exactly where it was placed, hadn't thought of it fitting anywhere else ..
It might be romantice to think that Ennis was dropping the girls off to spend a night with Jack, but I wonder, first of all, if Jack would have been all the way up in Wyoming for just a one night (actually part of a night) visit. And from the age of the girls in this scene, I really can't see how Ang would have thought this would be placed later in the story. This scene was also in exactly the same spot as in the screen play, too ... :-\ (, although I guess the sceen play could have been written published based on the final version of the movie rather than the other way around. In addition, Ennis would have shown up in his own truck at the grocery store, not in Jack's, otherwise tongues would wag. We DO see them getting in to Jack's truck together the morning after the reunion, however.
As to whether or not Ennis was devoted to his job, well, ranch hours are any time the stock needs your attention, so if the heifers were calving as Ennis tells Alma, it would have been necessary for Ennis to go there. He would have wanted to keep the job to put the bread on the table, as you say.
Much as we might find the grocery store scene may seem unimportant at first, it does serve to show too that even before Jack showed up again things were not perfect in the Ennis and Alma marriage. This is not my favourite scene by a long shot so probably don't pay much attention to the nuances .... There is also a big continuity error in this scenes (the peanut jars that get broken, first shot has a lot more knocked over than the later shot) which I can't seem to NOT notice every time ..

So, I can see where there might be conjecture about Ennis being anxious to drop the girls off to be with Jack, but I (personally!) just have a hard time making that fit.
But I guess that's what makes this scene and the whole film interesting, isn't it? Because it leaves so much up to the viewer, we can all see something different even though we're watching the exact same thing. You have to love that!
No wonder we're all anxious for that special addition DVD with the directors and actors commentaries .. many mysteries will be explained!