It is surely reasonable for someone to be given the delta cost between the cost of feeding him/herself at home and the cost of obtaining it at a Service Mess or commercial source when detached. But free? Definitely on Ops - but during courses in the UK? Hmmm......
If I recall correctly, the reason we didn't get charged for food at RAF Mount Pleasant was because we worked 6 days a week. Although the number of pongo Landrovers parked outside the Officers Mess on Saturday morning when I used to go to work would seem to indicate that not everyone actually did work 6 days out of 7. But it was good to do a nice low overshoot on the short RW over the Officers Mess to wake up the hungover brown jobs! The mighty Vickers WhisperJet is quite good at doing that!
As for whingeing beanstealers, try putting yourselves in the position of the living-out singly who has to throw out all the perishable food items whenever he/she is subject to short-notice detachment.....