This tip is for those who suffer from lymphoedema in their legs..
For those who are travelling (and not driving) - I found one of the most effective (and non-gimmicky) way to ensure that your leg is active is to simply wiggle your toes.
You'll find that you can actually get tired of doing for five minutes or so but I've gotten so used to it that I can do it continuously for 20 minutes and more.. Seriously I've seen these contraptions that you can get that you do various things with your feet and legs but I found that this simple exercise is the best.
When I was 7 - a nurse told me to constantly wiggle my toes. When I find myself in situations where my legs are still - I wiggle my toes. I'm pretty sure that this tip has helped with the healing of various operations that I've had in my life..
Start wiggling your toes!