Rule number one: always carry on your film. The checked baggage x-rays are definitely strong enough to mark your film, but carry-on xray machines won't hurt it.
To put your mind at ease, you can buy and process all your film while you are there, but it is really not necessary.
Re: the fellow above's statement that the carry-on machines are safe up to ISO 3200. The fastest films you can get, Delta 3200 and TMax 3200, are really only ISO 800-1000. How you rate them does not change the true ISO one bit, so even they are safe.
Interesting trivia re: x-rays: According to the data sheet for Efke IR820, there is more of a risk of ruining this film by bringing it out into room light than there is having it scanned by a carry-on baggage scanner (in 35mm, due to the felt's poor ability to block IR).