There is something that can greatly lower one's risk of deep vein thrombosis on flights.  Nattokinase, an enzyme of natto, which is made from fermented soybeans and is the base for miso soup, helps the body dissolve blood clots in veins, which is the cause (virtually the definition) of deep vein thrombosis.  It acts very quickly, so taking a couple of capsules shortly before a flight can make a huge difference.

Nattokinase functions by destroying plasminogen activator inhibitor, a blood constituent that prevents clot dissolution.  It can also be taken as a blood thinner, but without the risks of coumadin (warfarin) and other prescription drugs.  In fact, rather than simply thinning the blood, it directly allows clots to be dissolved, so blood function is not otherwise harmed.