I package up any leftovers and put them in single portions in the freezer. It makes easy to grab lunch options for later, plus I don't have to eat the same thing for 3 days in a row.
Salads are also awesome. In your tupperware container, start with your dressing of choice on the bottom, then add carrots, celery, tomatoes, cuke etc, working your way up the container with "drier" ingredients. Top with lettuce and close the lid. Dump upside down at work and voila, not soggy salad. I like adding things like pear, avocado, dried cranberries, almonds, goat cheese to give the salad interesting flavour. Add leftover chicken, or tuna etc if you want more protein.
I also like making a quick breakfast sandwich. One egg in a bowl with a dribble of water in it - nuke for 10 seconds at a time; top with cheese of choice once its almost cooked. Toast bread of choice while egg cooks; throw it all together with ham, avocado, tomato, hot sauce etc for a super tasty and filling sandwich. (I like english muffins and if I want a healthier bread, I use sprouted grain, which is more filling and has a higher protein content, higher fibre etc.)
Snacks include fruit paired with cheese or nuts; veggies and often celery with cream cheese; sometimes dried fruit; also frozen berries (raspberries, blueberries) or fresh when in season, in the bottom of a tupperware container, top with greek yogurt, then granola and shredded coconut (the granola isn't crunchy this way but I'm often too lazy to bring an extra container with the granola separate; also the berries thaw out by the time they are ready to eat.)
With my shifts, I often have 3 or 4 meals plus several snacks with me per day. This makes for big lunch bags, lol.