If you are an Orthodox Jew travelling and you are unsure if the food is kosher, what do you eat?

You find out ahead of time where the kosher food places are wherever you'll be going. This can be done by contacting a rabbi there, or even on the internet nowadays, for all the areas you'll be going through.

And you can always bring some snacks with you.

If you're going to be on a plane or something that doesn't offer kosher food at all, you can bring your own. There are even little tv dinner like kosher meals with their own little cooker in them now and silverware.

I ask a Muslim to point me out a Halal outlet, cos in Israel we eat each others food

Vegetables. Very religious Jews can't even have non-kosher milk.

If you're an Orthodox Jew traveling you already know where the kosher restaurants and grocery stores are--however if there is some emergency, vegetables. You eat vegan for a while (yes I mean vegan) until you can find kosher food.

You plan ahead. There are many websites where you can find the kosher restaurants in the area your travelling to.
During our last vacation, we actually rented an apartment and just took our food with us. Once there, you can find a supermarket to get products that are kosher as well as fruits and vegetables.
Most cruise lines also offer a kosher menu.

Buy packaged food in a grocery and check if it has a reliable kosher symbol.