Just a suggestion, but have you thought about doing something easy like substituting a healthy cereal with low-fat milk in for lunch? For the calories you have there, you can have a double serve and STILL have half the calories. And you'll have a lot more fibre, which will fill you up and make you feel healthier AND it's cheaper.

(I know, breakfast food. But it's easy for lunch and you can keep it at work without needing to fridge it)

You're doing really well!