1. Drink a lot on the flight. A lot means: you have to pee every 2 hours. Urine has the color of white wine (not the color of beer).
Almost everybody on a plane doesn't drink enough and is dehydrated. A lot really means a lot.
2. Keep the leg elevated, i.e. fly business class.
3. Wear graduated (explained by another poster) compression stockings. Not the cheap stockings the airlines sell.
4. Walk a lot during the flight. Every 20 minutes, as Lacessit said.
Flight attendants won't like it. Ignore them. It's your health, not theirs.
5. At check-in, take one of your Eliquis. OR take a prefilled injection of Clexane 40mg as described by others (only once, shortly before the flight, not every 3 hours). Not both. No Xarelto ( you said you still have Eliquis), no Warfarin.