Travel Health and Fitness - How do you strengthen your stomach for travel?

I think the answer is to travel more, and expose yourself to more risks--but is their an easier way to prepare and strengthen your stomach for travel? I have a very sensitive stomach and I met these guys while traveling--they were all American but all born in other countries--and they claimed that they could eat anything and it didn't bother them, but their American-born-and-bred friend was sick.

Any clues?

Thanks

Are you saying the American born friend had food poisoning, was sick in general or had some type of allergic reaction to perhaps something he didn't normally eat?

Cheers.