“What foods to avoid before the flight?”

First thing that comes to mind are "flatogens". Examples are beans, cabbage, brussel sprouts. These great gas when digested and with the reduced atmospheric pressure when aloft you will be uncomfortable. Fried foods can cause heartburn and contain high sodium. This can lead to bloating and swelling. Don't overeat. Dehydration is an issue aloft, so avoid any caffeinated drinks or alcohol-even if you are a passenger. Obviously, pilots don't drink alcohol many hours before assuming flight crew duty.