Rife in some areas into privatisation. Not just sandwiches. Staff would go to a cash and carry, load up with cans of lager etc. then sell them on the train for the price the railway charged and pocket the difference. Football Saturdays were strangely a very popular day to work - contrary to what you'd usually think!
They'd sell wine to standard class passengers, pocket the money, and put it down on the sheet that a first class passenger had been given a complementary one that they were entitled to have.
Got told all this by someone who once worked on buffet cars and I was astounded!
Having said this, I know from personal experience that there was a tough process to go through if you did things that looked like you had pocketed stock or cash. I recall an occasion early in my employment when due to a large queue and being distracted at the till, I can't recall the exact error, but it was something like I keyed in a sum for a product (cup of tea I think) at say 40 (pence) but the tills registered products by item (so the till clocked 40 cups of tea at eg 40p each not one cup at 40p) - result: till about £15 'down' at the end of the shift - tills were not shared so 'your' till was your responsibility. A till could take several hundred pounds during the 8 hour shift so this was not a large percentage of the takings. I didn't notice the error and forgot all about it. However, this resulted in a detailed cross questioning by the shift supervisor who had to cash up the till, and then an interview with the manager next day when they came on duty. Fortunately by that time I had worked out what had happened and was thus able to offer an explanation. This had to be written up and signed by me, then sent off to a higher person (probably a finance officer or regional office or some such). It was made clear to me that if the explanation was not accepted I could be up for disciplinary action etc. I suspect that it was accepted with no further action, because if you had wanted to steal £15 you would not be foolish enough to leave an obvious trail on the till records!
Funnily enough, and I could never work out why, but it seemed impossible to ever get your till to balance correctly at the end of a shift. It would usually be up or down by £1 to £2 however much care you took - which does mean that people do get the wrong change on a regular basis! Those sorts of sums were accepted however.
So clearly such matters were treated seriously. But that's not to say it would not have been possible to steal items of stock and material, or perhaps find ways to sell products off the books - although that would be tricky at a station outlet (whereas I think trolleys on board would have operated with no more than a cash drawer, not a till, which makes it easier).
