zahavasdad,
Do NOT bring MRE’s onto the trains without asking. It might set off smoke alams or scare other passengers especially with the smoke
I agree that it’s a good idea to ask first, but I don’t think that self-heating MREs produce any smoke. They use a chemical reaction that heats the food to not much more than 100 degrees F. The kettle is much more problematic due to the required voltage and temperatures (but they don’t produce smoke either).