Label your box
Placing a label on your box can deter some of your coworkers from stealing it. The label should clearly state your name and the fact that the lunch box belongs to you. This will also rule out the possibility of someone mistakenly eating your food.
Add a warning to the label
If the name label does not work, you should add a warning to it, stating that anyone stealing this lunch box will be reported. To make it clear that you are serious, put the warning in red color and bold font.
Spike your lunch with laxatives
To deter the more persistent lunch thieves, you may have to resort to more drastic measures. Spike your own lunch with laxatives one day and let it be stolen. Hopefully the thieves will learn their lesson and will think twice before stealing your lunch again.
Lock away your lunch box
If your work place has a separate kitchen with cabinets, find one which can be locked and use it to secure your lunch box.
Use camera recordings to find culprits
Some offices have cameras installed which record daily proceedings. Apply for a footage review to find out who steals your lunch. Report these people to human resources.
Stop bringing good food
If all the methods above don’t work, you should stop bringing delicious food. You may have to start bringing ordinary bland tasting lunch for some time to deter the thieves.
Place your lunch box on your desk
If you have space on your work desk, you can put your lunch box on it and cover it up with paper. Don’t leave your desk for prolonged periods, and if possible, ask a trusted co-worker to keep an eye on your lunch while you are gone.
Quit the job
If nothing else works, you must quit the job. Being unable to deter the thieves, this may be your last resort. Look for another more secure work place and move.