It's a very good idea. It's no fun trying to find a chemist that is open at 3am in a country you don't speak the language of. It only takes that happening once before you realize it's worth the small amount of space required for a few packs of condoms.

And to add to the original conversation, one of the things I always pack with me are anti-diarrhea pills. I've only needed them a few times, but they are crucial when you need them.