One more practical and non expensive idea is just keep a weighing machine and ask your staff to weight the food wasted every day and you could ask them to report you every day, you can display on the white board amount of fodd wasted every day throughout the week and reflect that the amount of food wasted would suffice for how many people. This leaves an impression on the mind and the cost and time spent on the same is bare.
People genuinely tend to feel guilty and practically i have seen difference in wastage.
Regards
Swapneel