I travel light, so when packing only for myself and not for the whole family, I opt for only carry-on luggage. The yoga block goes into the suitcase and the tennis balls to a carry-all type hand bag. Both the yoga block and the tennis balls are easy to pack due to their light weight.
So what do I do with my props when travelling? My all time favourite is to just lie down on top of a yoga block. Travel schedules can be crazy, so the practice needs to be simple enough to get it done. This particular one does not require much energy so it is doable even at the end of the most tiring days. And it works in the yummiest way to open the upper back and chest to counteract all the sitting, and slouching. The block can be positioned three different ways to provide different height and intensity. For a relaxing, gentle chest stretch try laying the block flat or on its long side, i.e. either one of the two lowest positions. For more intense stretch, stand the block on the short side. Place the block underneath the middle back/shoulder blades and experiment with different arm positions, extending the arms over the head or to the side, and just breath and let the body do its magic. Stay a few minutes and come back slowly and do a counter pose, eg. Balasana/Child Pose.
Another one is to place the block under the sacrum, the bony part of the back hip. Keep knees bent and feet on the mat or extend legs slowly, one by one. Make sure there is no excess pressure on the lower back; the lower the block position the gentler stretch. To get out of the pose, bend your knees, feet on the mat and slowly lift the hips up so that you can remove the block. Lie down on the back for a moment and then hug the knees and maybe roll from side to side a few rounds. Again, simple, low energy practice that can really make a difference on how you feel. The pose stretches the hip flexors and can also alleviate stomachache/bloating.
The tennis balls are handy on the flight itself, providing relief to sore muscles even in the tiniest economy seat. I have my tennis balls typically within a sock - what a great way to reuse all those mysterious spare socks! Two balls in one sock and a knot so they do not fall out. One plain ball works equally well. Place the tennis ball(s) under the hamstrings, behind the back or under your foot, and create pressure and make some movement or just stay put. Voila! You will be surprised on how good a tennis ball massage feels, beware massage therapists! The tennis balls are equally, or even more, usable outside of the perimeter of an airplane. The logic is simple, place the tennis ball under the area you want to massage, create pressure and either stay put or move on top of the ball. There are loads of tutorials available in the Internet, go google and experiment. Remember that pressure is on the muscle, not on bones, blood vessels or nerves. My personal favourite is to roll my back, especially in between the shoulder blades, on top of two balls. The balls can be placed on the floor, or on a block for more intensity.
I hope you find the above tips useful! For me, this is not only something I do when travelling, it is my daily routine to keep my back and shoulders happy wherever I am.