I’ve done seven long haul flights with my LO - my top tip is to just think in terms of each 10 minutes. So have several things to play with and rotate them (not just toys - paper cups, plastic bottles, spoons etc.). If you only worry about the next 10 minutes then you aren’t focusing on how to keep them occupied for a whole flight. Also it means that naps use up lots of 10 minutes which is always very enjoyable. Don’t expect to get to watch a film though 😫
Not that I've done this, but have friends who wrap little toys as presents for the trip which they highly recommend. Can be a few little things where they open one before and one or two during the flight. Presenting them as presents makes it a bit more exciting and they tend to be interested in it for a bit longer. Can be anything like a little book, toys, colouring book/crayons etc. Other than that, plenty of snacks 😁