I worked MkIII and HST and stock levels were still limited to a certain degree, if its busy I wouldn't double up beers untill everyone has been served for example.
I can't comment on what others may have done but to the best of my knowledge we always worked send out drinks, send out food (on the all day offer) or head back to the kitchen to help serve the resturant meals, once the food had been served then bring back the drinks.
There are areas I am not allowed to comment upon but back in MkIII days there were less set swaps, so the set I boarded in the morning was mine all day. I also used to work regular diagrams so I would know that a certain train in an evening had a good take up on white wine or if the restraunt meal service was steaks then keep a good supply of red wine.
Believe it or not I don't like to say no to people and also recognise that bums on seats keeps me in a job but if you are told one only, or a drinks trolley goes out and straight back, there may be a good reason why.