Every so often the owner would come in and say "no more house pies [making one pizza per shift to share amongst the employees]", every so often they'd crack down on saving mistakes that had been cooked already and say that we had to throw them away. I would often dig them out of the trash when the managers were busy, or slip a menu item into a box, a bag, or even a paper towel and tuck it away. This was pretty common. Also I would often team up with a comrade who worked there and we'd take all the fully cooled leftover lunch slices to our social center.
Other people would be more brazen and literally go in to cook a bunch of food for themselves before their shift or before break.
Part of what made that job so easy to continue with was that it was a 6-minute jog from my apartment. It's a well established restaurant and losing a little bit of prepped ingredients here and there, even if done by all employees, wouldn't even touch their bottom line.