Food at trains

Just curious what kind of food is okay on long distance trains. Most common seems the cold served bento boxes but once I experienced an american couple eating pre heated pasta something like the ones from Lawson.

It smelled of hot food in the whole car and I heard them whispeering things like getting dirty from the pasta sauce.

Does japanese people bring hot food as well?

Any food is okay except excessively smelly food, such as McDonalds hamburgers and the pasta described by you. I don't think there is a rule even against smelly food, but it is polite not to bother other passengers with excessive smells.

strong smell food is not happy for the other passengers as common sense

At Tokyo station for example I have seen food stores that sell hot bento to go, or a bento box with a special heating pack at the bottom (you pull a cord and it mildly heats it up), so it is not that ALL hot food is not OK.

But I would avoid things like McDonald's burgers and fried chicken for their smell, pasta and other drippy items for their possible stains/mess on the seats or floor, or extremely crumbly snacks and things for the... crumbs obviously.

It's nice to say "avoid smelly food for the sake of other passengers", but the train staff themselves actually sell dried ika (squid) snacks which STINK to high heaven. I rode green car on the shinkansen from Tokyo to Osaka with that strong smell near me the entire time... it was awful! Eater: Japanese salaryman.

In other words, what stinks to some people doesn't to others. So do try not to eat super smelly food, but in reality people eat whatever they want. So don't worry too much about it. There's no written rule.

Actually, locals eat lots of smelly stuff on long-distance trains. And while you don't see much Mac and KFC on those trains, just because there are better treats, you do smell them inside movie theaters and also on local buses when people simply carry them to eat at home. So at least it's not "uncommon."

And as mentioned, it's absolutely normal to eat heated food on long-distance trains. There even are eki-ben (station bento) that are designed to be heated at your table. If someone was whispering about pasta sauce, I think that person was just doing that for fun. There are a lot of train food that have the risk of being spilled and stained.

But hey, the ride is only for a few hours. You can try to wait until you reach your desination to eat smelly or spilly food. On a related note, a lot of people tolerate their hunger just so that they can eat regional specialities at their destination, such as soup noodles at platforms.

When I travel by train I plan according to where I sit (window or aisle) and how many people are in the train car. Also there are cars I have seen that are more secluded than others coming to seating (the Kirishima I think it was from Kagoshima to Miyazaki had a bit of sectioned off part in the car or what to call it).

I seldom eat when in an aisle seat or in a full train, unless I have not eaten since very very long. I just want the privacy, not like having people reviewing my eating technique with hashi...

But still to the OP I would recommend regular bento boxes or sandwiches. The later might be having sauce in it but often comes with plastic wrapping.