I have put my lunch in the icebox at work and when i go to lunch someone has taken a few things out. What can I put in it to stop them?

As tempting as it is to somehow spoil/contaminate the food (even laxatives etc) you could be in serious trouble for doing so. If this is a one off thing, it is possibly a genuine mistake. If it is an on-going problem I would raise the issue with your manager and request them to speak to ALL staff about it. Consider keeping your lunch by your desk (if possible) so at least your lunch remains untouched.

If you insist on taking te revenge line - I would either go for an unpleasant taste (a sharp pickle or something) that will just taste bad (not painful, not stupidly hot etc) or just putting a label on the food saying "Dear Food Thieft. I may have added (insert unpleasant ingredient) - do that a few times and taint the food. The thief should stop.

Or just put a note up in the staffroom saying that food has been going missing and you will happily bring in extra but just to inform you all that the (milk was breast milk - or other weird/disgsuting ingredient)

The best way for everyone though is to talk it out as a whole office - sometimes mistakes happen. You think you packed an apple but there are only oranges in the fridge. You assume you were mistaken and have an orange. Turns out you never packed your fruit and you find the apple at home on the side. Accident - easily sorted out by brining in an orange with a note saying "sorry, I ate your orange yesterday by mistake"

If it is a petty person or an ongoing problem, leave it to management to address and deal with

We had a similar problem at my work last year. Someone was taking bites out of lunches, and putting the rest back. It ended when this young guy basically ground up ghost peppers, and sprinkled them onto his slice of pizza he was leaving in the fridge. A few hours into the day this woman who worked there had to go to the hospital from the pain of biting into his pizza. Needless to say she never returned to work.

First and foremost understand that if you intentionally poison your lunch then that can get you into trouble. You'd have no way to explain to the police why there happened to be rat poison in your food. So please, don't do anything like that.

With that said you could still make eating the food a miserable experience for the thief. You could try hot peppers, like my friend did. Or you might bring in trail mix made with chocolate laxatives. If you trust leaving it out you could also set your phone to video record and leave it hidden someplace where it has a view of the fridge. Even with 8gb your phone should be able to record until your lunch.

Good luck.

Take a bite out of each item before putting it in the refrigerator.

Get a box with a lock and keep the key in your pocket. And make a bit show of it, say you have to do this because your office has thieves in it!

Put something in your lunch that you know the thief likes. Once it is taken, inform the office that you put special medication in that item -- medication that can make a healthy person incredibly ill. See what happens.

Someone did this in an office in which I worked. Someone else kept stealing his soft drink from the fridge, so he started putting the bottle in the fridge after unscrewing the cap and then screwing it back on. After a few thefts of the opened bottles, the guy sent out a broadcast email stating that he had been lacing his soft drinks with his medication, and that the thief should probably see a doctor.

Put sellotape all around it,

A mousetrap!

Better still, add purgatives to your lunch and leave it in the icebox (of course, without a note).

put a note in it, saying you have strep throat, and have already licked all the items.