Get yourself a tennis ball, a pair of socks or anything which might squeeze in your hands. Start squeezing them with one hand at a time and keep doing it until your wrist is tired. Notice how it has helped you build your forearm muscle.
Put your carry-on bag on your thighs and start raising your legs with the help of your calf muscles. This seems pretty easy at first but once you start holding your knees in mid-air, with your bag on your thighs as well, you will soon grow tired. Once you do get tired, you can stop this exercise.
Put your feet on the ground and lift your toes up, with heels sticking to the floor. Stretch your toes as much as you can. Keep repeating this exercise until your ankle gets tired.
Put your hands on your armrests and start raising your knees slowly. Doing this with both your hands will help you burn more calories. Keep raising your knees until you touch your chin. Keep doing this exercise until you grow tired.
Cross your legs and start rotating the dangling foot in a circle position.
Keep your chin close to your throat and then tilt your head forward and backward. You can also roll your head from one should to another. This will help you with the everyday neck exercise.
You can also flex your trapezius muscles. In order to do that, you must work your shoulders. First lower your shoulders and take them as low as they can go, then raise them and bring them up to your ears. Repeat this exercise till you get tired.
Arch your torso forward like a cat and then move forward and backward in order to work on your back muscle.
Lastly, flex your gluteus muscle. In order to do that you must move your rear to the right and then to the left and stretch it as much as you can in the small area which you have been given.