This might be why the trip leader might think it's going to be a problem.
http://www.guineapigcages.com/forum/283020-post17.html
However, I wouldn't simply assume the people there are too dumb to understand why you'd reject their food. I don't know about you, but I'd rather starve to death than ever eat another animal. I'm assuming there will be a translator for you who can explain to them why you won't eat meat, so if you write up a few short paragraphs explaining your beliefs, everything should be fine. Make it clear that you're not rejecting them and you appreciate their gratitude, but you're not willing to compromise your own beliefs either. If they still get insulted, then so be it. All you can do is give them the opportunity to try to understand, and if you do, I think you'll have a good chance of getting positive results.