Welcome Back Mrs. E! The pictures are fantastic... the weather looked lovely, warm and sunny -- but then that's Vegas, Baby.
6 pounds is not bad for the US (you are right about the portion-sizes), and you are probably retaining a little water from the flight.
jlm, I kept my weight gain down whenI was in Florida for three weeks, by bringing one bar for each day and a shake... then limiting myself to one meal out and trying to be careful about my choices and portions (but, not too careful). In three weeks I gained about 7 pounds, I think. But, some of it came off very fast w/o dieting which makes me think I was retaining some water.
But, don't let the diet ruin your holiday... and try hard not to let the holiday keep you from "getting right back on the horse."
MM