Why do my ankles swell up so much when flying? what can i do to stop this as it looks awful on the beach!

Feet are dependent: While sitting. Try wearing support hose and walking when possible. Don't have salt with food on flights.

Support hose: You are a bit young, but could simply be fluid accumulating in your legs from having them "hanging down" and not moving during the flight. Wear compression stockings (20-30 mm hg) when flying and move your feet + legs periodically. Stay hydrated. Given that you are on zantac (ranitidine) at 30, i suspect a dietary/metabolic issue issue as well. Zantac (ranitidine) can deplete mg - consider supplement. Good luck.