If you have access to a freezer and microwave at work, you can buy some low calorie frozen dinners to take with you. These would depend on your individual tastes.
You can get whole grain bread (or wraps) and keep sandwich fixings on hand, such as deli-sliced turkey or chicken and pack sandwich ingredients separately, then make your sandwich when you are ready to eat. The same thing can be done with salads. Sandwich and salad ingredients often tend to get soggy or not so fresh when put together for any length of time; by packing the ingredients separately, you're making it fresh. With a sandwich or salad, all you'd need to include is maybe a yogurt or piece of fruit. Breakfast items could be a whole grain cereal with fruit, whole grain toast with peanut butter, yogurt, hard cooked egg.
If you can give us a better idea of what you like, we might be able to come up with recipes for you. You can make bigger batches of foods on weekends or when you have extra time, then package them in individual servings, so all you have to do is pack it up and go. Of course, as stated above, that depends on whether you have access to a fridge and microwave at work.