Walk around the airport during long waiting periods.
If you’re at your gate an hour early, have a delay, or have a long layover, those are perfect times to get a little exercise in. Take your stuff with you and walk around the airport.
Carrying your luggage around may be tiring, but it will also be a good workout. Additionally, walking around can help you loosen up your legs so you won’t feel so fidgety on the plane.