On long trips in a car or an airplane, it is important to get up and move when possible. Some ideas to relieve travel-related tension:
Rag doll - Separate the feet at least hip-width. Fold forward, bending the knees a lot, and hang from your hips. Arms can dangle, grab opposite elbows, whatever feels best. Consciously relax the wrinkles out of the back of your neck. Breathe in, think about creating space between each vertebra, and releasing tension with each exhale. Hold for 5 to 10 breaths.
Legs up a wall - Lie on your back, feet pointed toward a wall, or other stationary surface. Scoot your hips close to the wall, walking your feet up the wall. The further away you are, the more you can bend your knees/shorten the angle to experience less tension. The closer you are, the more intense the stretch. Feel free to place a pillow or the like under your hips for comfort. The rest of the body is relaxed. This pose is great to relieve swelling in the legs from prolonged sitting. You can even do it in a quiet corner of the airport during a layover! Hold for one to five minutes. Breathe deeply, exhale completely.
When you can't leave your seat, you can use reciprocal inhibition- in this case, isometric contractions of the abdominal muscles to facilitate relaxation in the muscles in the low back. Sit tall in your seat and take a deep breath in. As you exhale, contract your abdominal wall inward toward your spine, then imagine you can draw your navel up and under your ribcage. Relax, repeat five to ten times.
Finally, you can counter the seated slouch by reaching forward, and grabbing the top or sides of the seat in front of you. Keep you head in a neutral line with your body. Inhale, visualize reaching your heart and tailbone in opposite directions. As you exhale, allow your chest to drop toward your knees (as long as it feels good in your shoulders!), feeling a stretch in the pectoral muscles, the intercostal muscles, and experiencing release along the spine. Inhale to extend, exhale to sink and soften. Repeat three to five times in a row.