Where the heck should Ennis have put more furniture? The trailer is full. Other, better furniture, yes. But more?
I think Alma Jr. is speaking in polite code for "Daddy, you need a home" as in "Daddy, you need a life". The stuff in Ennis's trailer looks like the accidental leftovers from a garage jumble sale - decrepit lamps, random odds and ends including that block of knives, broken stuff that has been kept on the odd chance it may one day be mended.....
Except for the hidden little Brokeback shrine the trailer's interior is impersonal, cold, indifferent, can be left at any time without a backward glance. It's not a home, it's not the frame surrounding an actual *life*, it's a place to exist while the days go by. It's downright scary to think that Ennis actually lives there.
You're so right - the first picture is so sad it hurts!
If I were a spiritual person I'd find it extremely painful to imagine Jack looking in on Ennis from some other reality, and seeing that first image or other moments like it.
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Lee, I'm with you in surmising that Ennis rushes off for some Jack-related alone-time when he leaves the kitchen with that purposeful stride after having re-read the postcard. Partly so as to not have to come up with more lies to answer Alma's queries, but I agree it's mostly to be alone with his thoughts and memories of Jack, - letting himself imaginine the upcoming reunion. And it's a very short step to including the line you're quoting in the likely scenario.......