It may sound strange but I always try and take either lavender spray or Olbas Oil for long sectors (under 100ml, of course). I find the cabin air to be very dry and the lavender or Olbas oil allows me to relax and breathe well. You'll get an amenity kit to help you moisturise but your tired eyes will feel a lot better if you also consider eye drops or a good under eye gel/cream. I know all this might sound over the top but it has helped me feel human after a long flight!