Believe me, rain, I've tried every combo going. I've been doing this journey in many combos for a very long time. I'm very well-versed in what works for me and for us and pack our hand luggage accordingly with such precision, even the attendants remark on it. It's usually 40 degrees or near enough with sky high humidity in Houston when we land and even in the airport, it's boiling hot to us and we've been on the go for the better part of 18 hours. It takes at least an hour to get through immigration, even as US/UK nationals, which we all are, baggage claim and then the further queue after baggage claim. I want to wear shorts, a vest top or tshirt and my Reef sandals on landing, because my feet are always swollen by then despite flight socks and moving around. I'm not interested in stripping off layers to do that except in the lav. I'm well-practised at it and it works just fine.
Our flight from either London or Europe is nigh on 10 hours and we've have to fly from Glasgow and then change planes every time, so it's a very long journey, especially with an autistic child.
People are just sharing what works for them. If others don't have such requirements, good on them. I'm just sharing what works for us. Layering doesn't do it for me. I've tried. I have a pair of shorts, my Reefs, and a top in my bag and go into the lav and change into them. On the way back, I wear clothes appropriate to what the weather is like in London or Amsterdam and then change into clothes for Glasgow if necessary.
I don't bother packing jackets because DH collects us with the jackets and if we get stuck in London, we'll go to a friend's and then get on a train and go back to Glasgow.
We have a 2-hour drive from Glasgow.