Issues with flying are usually because of EMF exposure, wifi, time zones, toxin exposure, radiation exposure, dehydration and hypoxia (low oxygen). Some people seem to be more sensitive to electromagnetic frequencies and radiation exposures. For those people, it’s better if they don’t fly if they don’t have to. You can research some EMF reducing wearables

You can try to get ‘the pat-down’ instead of X-ray machines.

Use hydrogen (H2) tablets in water before flying  and every 2-3 hours in flight.

Airports and their restaurants routinely use tap water. Avoid drinking that. Buy bottled water once you get past security. Take time to walk during layovers to keep blood and lymph flowing. Fasting is amazing for keeping inflammation and oxidative stress at a lower level throughout travel.

My Travel First Aid kit includes: 

Digestive enzymes

Ginger caps/chews

Magnesium

H2 tabs

Charcoal

Melatonin

Liver support