A salad that will stand up to 6 hours of air travel

Something like this massaged kale salad would be perfect- i would do the massaged kale, pack the dressing seperate. For toppings the beans that are part of the recipe sound great and would be fine. I would also add some sturdy chopped veg like bell peppers, carrots, broccoli, etc and some nuts or seeds.
I like to use a leftover lettuce bin or large jar that i can recycle after using as the container.

Another option:
Baguette sandwich- or use other very sturdy bread. Spread with a soft mild cheese like chevre (fresh goat cheese) on sliced bread both sides. Inside add jarred roasted bell pepper strips, chopped olives, and/or jarred marinated artichoke hearts. Cut sandwich into easy to eat pieces and wrap really well.

I would take components that are easily opened and/or combined shortly before you want to eat, things that don't themselves or in combination promote dangerous bacteria.
Dried meat (jerky), whole raw veg or fruit that can be eaten or cut easily in air (celery, tomato, cucumber, apple, pear), aged dry cheese, whole grain crackers or bread, cooked beans (legumes, though green or yellow beans would also be fine), small bottle or thermos of iced coffee, wine, or fruit juice. Generally, for consideration of others in close proximity, avoid smelly cheeses or most preserved fish.

Another kale salad that I love and should
survive your 6 hours of travel is https://food52.com/recipes/15584-northern-spy-s-kale-salad

A salad with kale.

Example:

https://food52.com/recipes/26166-perfect-kale-salad

https://www.epicurious.com/recipes/food/views/mediterranean-couscous-and-lentil-salad-51129890
Keep the arugula, tomatoes and feta in a separate container until you're ready to eat.