How about this:
1. The mess runs as it did previously. You are not 'rationed' as to how many sausages you can eat, etc. Food charges remain as they were.
2. You take a meal in the mess, you sign for it.
3. At the end of the month, you are charged (through pay) for those meals you have taken. You do not pay for meals you have not taken.
This is what everybody thought they were getting when PAYD was first mooted.
Yes, overall reciepts from food charges will drop, but the mess will soon enough figure how much food to stock / prepare to prevent waste. If the above somehow leads to not enough money being put into the food budget, then we have, somewhere along the line, been scammed for years.
BINGO! - so THAT'S why they didn't do it this way.....