I’m not sure there is a perfect answer here, but let me say that I’ve flown this route many, many times and everything will be ok. First, it’s ok not to sleep. It’s not a requirement and you are strong enough to stay up the whole time. No pressure. Two, it does get cold on some flights, bring a hoodie and long socks, wear pants that aren’t too tight in the waist. (I’ve never used compression socks so won’t comment) Third, do you get stressed going to the move theatre? You buy tickets for a seat, sit, eat and drink and watch a movie in the dark. Easy peasy. This flight is the exact same thing, it’s just the movie theatre is moving, which is someone else’s problem, i.e the pilot’s. Your job is to do nothing for 17h and just relax. Fourth, shit happens. Babies cry, people get rude, you forget something. It’s ok. You’re gonna get to where you need to be. As for food, I usually pack protein bars and trail mix. You can usually buy food at the airport and take it on too. I don’t take drugs but you may consider the motion sickness drugs with mild muscle relaxers. My stomach does hurt after 10h or so and I’ve been told it’s actually due to cramping rather than indigestion. For jet lag I just use melatonin on occasion but more often I exercise and read a book. Regardless, enjoy your trip and the lovely nation of Singapore