I have an insulated lunchbox - I bring breakfast and lunch to work in it every day. Breakfast is usually plain low fat or fat free cottage cheese or yogurt with sugar free jam added. Or a Zone Bar....just make sure to check the calorie counts on bars - I look for around 200 calories with like 15 g of protein. I love Laughing Cow cheese, too or low fat mozzarella cheese sticks. I often have frozen LeanCuisines or Smart Ones, again watch the calories and sodium. I bring fruit and a salad as well...have I mentioned I like to eat?
The point is to always have healthy choices so you aren't looking for what to eat when you are already hungry.
An hour and a half break sounds like a good time to take a walk.