The Cadbury vending machines that were on almost every London Underground platform back in the 1990s and early 2000s were a favourite of mine.
Those are the ones I described above that were installed on the opening of the Jubilee Line Extension in 1999.
As I understand it, the machines were installed by concessionaires, who stocked and serviced them, and collected the proceeds. Nothing to do with the railway apart from a, probably small, rental. The refrigerated milk machines, etc, would need an electricity supply on the station, which probably increased the rent.
Older members here may also remember the "print your name" machines, where a large alphabet dial on the front, plus an appropriate coin, printed up to maybe 30 characters on an aluminium strip. It appeared not to need an electrical supply, each character needed the handle pulled to make the letter impression. Some years ago, visiting the Bluebell, I got into conversation with an older couple, who said they were not particularly interested in the railway ride, but had come specifically because they recalled such machines, and wanted to print a number of aluminium tags for their garden plants, and thought the preserved railway would still have them. I explained the bit about the concessionaires, who owned them and took them away. They seemed a little disappointed.