I will be in all these places for work, traveling with a group, with absolutely zero possibility of traveling by myself. I will be bringing some supplies, of course, but we are on the road for 3 weeks, and I'm only allowed one suitcase.

I don't even know how to say "gluten-free" in Spanish!!!

Any suggestions on food that travels well? We will be on buses and trains during meal times. I'm not TOO freaked about restaurants--I plan on getting arroz con pollo and salads whenever I have a chance to go to a restaurant. It's all the times they expect us to find a sandwich to bring with us on the bus or train that have me worried.

Any suggestions?

I don't know anything about being gluten-free in Spain. What I do know is, that the trains in Europe have restaurants on board (hopefully not only for first-class passengers, though). Also, every larger train station has at least a store to buy snacks (well, they do in Germany, anyway), many of them will have a restaurant for take-out.