I have learned to take food with me when I go to work. This means breakfast, lunch and snacks.
Does this seem like a lot to you?
Think of it this way, do you eat breakfast before you leave for work? I don't, I leave too early and food is the last thing on my mind. But, I know when I get to work I'm going to be hungry. By taking breakfast with me I'm "prepared" and will avoid the temptations that I might come across.
The same goes for lunch. Running out for a quick bite always involved "fast food". By bringing lunch, another temptation averted.
Snacks keep me going through out the day.
You might get some ideas by looking as some typical days I pack.