My healthy airplane travel / travel voice care routine includes:
Wearing a mask at all times on the flight not only keeps viruses and germs away, it keeps the air I breathe more moist. Great for immunity + vocal care!
A drop of Thieves (or Doterra OnGuard) oil inside the mask and under my nostrils
A drop of sesame oil or ghee inside each nostril periodically throughout the flight, whenever my nose gets dry
Drinking LOTS OF WATER with EmergenC (500 ml for every hour in the air, ideally)
Walking around the airplane and stretching regulary. (I book an aisle...