A couple of careers ago, I ran short line railroads. On a few occasions, we operated charter trains for local railfan clubs. On one trip, we had a combine with its baggage section set up as a snack car, with a counter, coolers, etc. They sold soda and various packaged snacks, as well as hot dogs. They did okay, but not great. The next time we did the trip, a couple of years later, the combine was not available, and instead we leased three coaches. The club folks had a couple of fellows carrying good-sized wicker baskets through the train every hour or so, peddling sodas and packaged snacks. They were sold out an hour or so before the trip was finished, and I believe they could have sold more if they'd had more supplies.
Of course, as mentioned above, selling soda and snacks means more cleanup and more trash, not to mention thoughtless folks throwing their empty cans and wrappers out the window. Someone would have to go through the train after every trip to clean up spills and crumbs, and the trash containers would need to be emptied on a regular basis. Any volunteers? Some serious consideration of the pros and cons must be given before embarking on this path. Personally, I favor no food or drinks on the train, but that's just me.