Maintaining a healthy die is perhaps more difficult for office workers than anybody else, as it is the norm to buy your food from a nearby shop. This can make a healthy diet very difficult to maintain because resisting the unhealthy food is a lot more difficult when it is right in front of you.
Bearing this in mind, the best way to actually manage your diet is therefore to avoid a convenience store altogether, and instead you should prepare your meal either in the morning or the night before; whichever is more convenient for you. This allows you to make a balanced, portion controlled meal which will keep you going throughout the day without actually compromising a healthy lifestyle.
A couple of good ideas for food during the day is a fruit salad or normal salad. Trying to include a little bit of protein is a good thing, but limiting it is ideal as you’re unlikely to be active during a day at an office.