When you're on a plane it can be hard for a Diabetic to keep their feet moving. Try to do little exercises while you sit, like moving your foot up and down or turning it in circles. Keep wiggling your toes to ensure your circulation gets blood right down to your tippy-toes.
Find out if there are any public gardening areas near you where people grow their own produce. This is an excellent way for a Diabetic to get some exercise by doing weeding, watering, or planting new seedlings. Often you get to keep some of what you grow as well, giving you some wonderfully fresh and organic treats to enjoy when you get home!