Fortunately, these habits are as easy to break as they were to create.
I used to watch videos with a group of friends back when I was a student. If I see one of those films now, I am taken right back to a world where haagen daz icecream and salty popcorn existed. I even used to pop the popcorn, if I was hosting the bunfight.
But now, I have other contingencies in play, and am busy laying down new traditions.
Chorizo crisps and cream cheese dip
pork crackling or slivers of crisp belly pork
puffed cheese blobs
Or
(and this is the easiest) time the film for my evening meal, and eat a nice big plateful at the beginning, and then forget about food for hours)
In your situation stuck on a train, I would just organise a takeaway coffee with lots of cream.
I have never yet met a carb craving that survives a hefty LCHF snack.