Drink plenty of liquids: Traveling is exhausting, especially with time zone differences, so drinking water is essential. Don't start a vacation depleted.
Have multiple sources of entertainment: Sometimes, the inflight service
sucks. Download all shows, movies, and music beforehand as a fallback option.
Bring extra snacks: Don't you hate it when you're so hungry on the plane, and it feels like an eternity before the snack cart comes by? Don't suffer. Prepack snacks, and when the snack cart eventually comes around, eat those snacks too. Eat everything.
Noise-canceling headphones: Snorers, babies, pets,
obnoxious people, and extreme extroverts. I cancel all of them out. I like the AirPod Pros because they're small. In addition, I download white noise on my phone to block everything out.