You may also want to see if there is a policy against this sort of thing for your office. You don’t want to introduce a fire hazard (even if you think it’s harmless) to your co-workers (even if you’d want to), now do you?
There are several reasons why I would like an alternative to the pantry, among those that have already been mentioned – messiness, stinky fridge, dirty microwave, occasional theft or disappearance, but perhaps the most important reasons are that I am starting on a new food plan and (1) I’m more likely to stick to it if the food is literally at hand and I eat it before I get hungry for things I shouldn’t be eating and (2) I would rather not have my office mates see the tell-tale labels of the well-known food plan products.
There is, indeed, a rule against having appliances in the offices, but I was hoping that there would be ones small enough that there would not be a possibility of stress on the electrical system.
I’ve seen some really tiny fridges, just big enough to hold a six-pack, for example. I thought that they were battery operated. That would avoid any possibility of fire hazard, wouldn’t it?
Appliances like fridges are notorious for “dirtying” your electrical circuit with spikes when they switch on and off. I wouldn’t like to try having one on the same immediate circuit as a PC.
How about a little cooler? Igloo makes some nice, inconspicuous soft-sided coolers. You could get some of that ‘Blue Ice’, and keep your private stock quite nicely, safely, and conveniently.
That still doesn’t solve any issues regarding housekeeping – in general, eating at your desk is less sanitary than a lunchroom. The lunchroom counters and tables are cleaned and disinfected frequently. When’s the last time your desktop was? Of course, a bottle of cleanser & roll of paper towels is cheap, so there’s another solution.
I’m afraid I don’t have a good recommendation for heating your food in the office.
It doesn’t help you, but I have a relatively large (about 3’ tall) refrigerator that is, of all things, styled like a safe. People actually think it is a safe; it is black, with “Kenmore Lock & Safe Co.” written on it, has a fake combination lock spinner, fake safe handle, etc.
No one ever realizes it’s a refrigerator. The only problem I run into is people wanting to know why I have a safe in my office. 
If you’re concerned about the labels, get some (microwave safe) containers, and put the diet plan meals in them at home. Bring them to work in your Igloo soft-side cooler, and heat them in the microwave. Everyone will think it’s just leftovers, and if anyone asks, that’s what you tell them.