Liposomal Vitamin C will help your immune system when you travel. At the very least you should take a multivitamin when you travel and these are also very effective.
Liposomal Vitamin C are nano sized spheres of fat that encapsulate vit c and deliver it to your cells. Its more effective than IV vit C.
Take some of these a day to boost your immune system when you travel or take like 5-10 a day if you are sick.