My typical long haul flight survival kit, done NZ and Aus plus others of 12 hours or 12 plus 5 is -
Wear glasses not contacts, elasticated trousers (or at least loose fitting) socks and roomy shoes, a comfy bra, t shirt and a decent cardi or hoodie. (I also often wear a thermal vest as I find flights cold and I like to put a heat pack on my back as it stops it ceasing up). On boarding I take all of the airline stuff out of the pocket and put in my noise cancelling headphones, phone & ipad (in airline mode), my cushion neck rest and my travel kit = mints, water, eyemask, tissues and a trashy magazine. Put my hand luggage overhead but where I can get to it. Take the pillow provided and put in the small of my back unwrap the blanket and put it under me or on the floor (if it's not in the bag it doesn't slide around).
Now it's time to sit back and relax, reading my magazine and sucking a mint to distract me through take off. I then usually watch a movie through drinks service and then the meal. After the movie I try to think about what time it is in the country I am going to and if it is night I will try to sleep. To do this I recline the seat (this is fine after the meal) put on my eyemask, snuggle up to my cushion and I listen to a relaxing spa playlist or meditation music. I don't generally get into a deep sleep but it is the best I can do.
I am a nervous flyer and have to sit in a aisle seat so I can get up and visit the toilet about once and hour (helps with the DVT though). When I need to be awake I might watch another movie read books on my ipad or play games. I travel with my DH and often my teen DC we rarely talk.
Both Singapore and HK are great airports, I will go for a walk the go and freshen up, wash, clean teeth and sometimes change depending on my final destination. The get a coffee and maybe some food depending on how I feel before finding my next gate.
We try to go for flights that arrive early evening so we have time to find our accommodation, go for a stroll and pick up some snacks before going to bed. The snacks help if you wake in the night with the jet lag.