We have been to the Far East - HK, Singapore and Malaysia every year for the since the girls were babies. They are now 6 and 8.(I have family out there) Singapore Airlines are very good.
Normally, when we get on board and walk to our seats, I always ask the air hostess for extra blankets for the children and myselfas during the flight, the temperature can get quite cold. We all take off our shoes as soon as we board.
I always bring the kids a spare thick cardigan and they put it on after their first meal when getting ready to sleep. I put them in t-shirts and loose bottoms and trainers / sandals. It does matter as they take them off once on board.
I alway bring a spare set of clothing with me as when we arrive at HK / Malaysia or Singapore, its usually baking hot so I pack a spare summer dress and sandles.
For myself, it just a top and either comfy bottoms though I have travelled long haul in soft jeans or a skirt. As long as they are very comfy, its ok. It also have a warm cardigan - not too thin or thick. As i alwasy ask for extra blankets, I'm not too bothered. As long as I can also use that cardigan on holiday then its ok. They normally supply fluffy socks which we tend to put on immediatly on board,
I also prepare a small makeup bag in a see through pouch (as in Heathrow - we need to have that scanned) with all my makeup that I need to use to re-do my face. All lotions and liquids must be in small bottles under 100ml and that would be allowed to pass security. So that is, toner, cotton wool, moisturer, light foundation, concealer and lipstick. Also, I put in spare contact lense bottle with saline and another one with cleaning fluid. I also take an asprin before I fly.
The kids each take a very small rucksack with one cuddly toy, and maybe a book and some pens and some sweets. I carry 2 DS for them to play with and a mag for myself. My kids love flying now and so do I but not DH.
Don't forget to ask the air hostess for children packs WHEN you board the plane. It's a little bag with things to keep them ooccupied.
Hope this helps.