If I take my own lunch (which I don't do as often as I would like), the contents are basically the same as your lunch yesterday, so I guess our nutritional needs are different. Microwaveable leftovers sounds like a good idea, either frozen or left in the fridge from the previous night's dinner - I used to do that when I worked at a place that had a microwave in the staff kitchen.

Since you have a toaster, you could also try crumpets or muffins instead of bread, for variety, or vary the type of bread you use. Hot soup with Irish soda bread is hard to beat, for instance.