Every train station should be an airport-like mall instead of the ugly things we have today. I would easily buy my Starbucks at the train station. Imagine waiting for your train in some awesome bakery...
Over here all central stations in bigger cities have quite some shops and stalls around. If there's any type of stall it will always sell coffee and other beverages and some snacks/sandwiches. The smaller stations are usually unmanned and without shops or stalls, but there's also usually a handful of people entering or exiting trains so it's hard to turn a profit there.