The high prices of food at the cinema, cafes etc is common knowledge and it only takes a little thought and planning to avoid it if you don't want to or can't afford to spend the money.
Have to agree with that. It's no surprise that some places charge what you may regard as "rip off" prices. Luckily, as said, with a bit of forward planning you can avoid it all.
We travel a lot but wouldn't think of using a motorway service station for food, drink or fuel. We just do a bit of "googling" beforehand and make a list of supermarkets close to motorway junctions along the route. Last time, we stopped off for lunch at a Morrisons near Walsall (I think), which was within sight of the motorway. Excellent bacon/sausage buns for lunch very cheap and filled up with fuel at the same time.
Same with train stations - usually there's a mini Tesco or a Greggs or MaccyD's or similar within easy walking distance of most bigger stations, so it's madness to buy your food/drink in the station itself. Again, a few minutes googling and you can find what's close by.
In the old days before the internet and before iphones, then, yes, you were basically a captive audience on motorways and train stations, but nowadays, it takes mere minutes to google alternatives.
Yes, airports are different re the liquid prohibition, but you can still take your own food onboard, and you don't even have to buy it in the departure lounge, you can take your own packed lunch etc made at home or bought from the supermarket the day before.