Store the leftovers in the fridge in small, serving size containers that are microwavable. I use these Pyrex bowls and I'm happy with them. It's so easy to pop the serving size in the microwave to warm and pour into the thermos.
If you make something that has extra leftovers (for me I always have a lot of soups and chili leftover), freeze serving size portion in Ziplocks for emergency use later. They'll thaw overnight in the fridge.
Cut up fruit ahead of time and store in serving size containers. I have small Gerber bowls like these from when my daughter was a baby and they are the perfect size to store serving size fruits, yogurt, etc. On Monday morning you'll see about 8-10 of these bowls stacked up, ready to go for the week. I sometimes buy the pre-cut fruit containers at the grocery store - it's a great way to get a variety of fruit and skip all the cutting time.
I like to use the weekends to make hummus and other sandwich items to fill in with during the week. I try to always keep Pyrex containers of sliced tomatoes, onions, black olives, and lettuce in the fridge. This makes it easy to throw together a healthy sandwich or salad (for your kids or yourself).
These Wholly Guacamole packs of guacamole are great for single-size portions - on a burrito or my favorite, as a dressing for a taco salad.
It might seem like a lot of work, but it really is just about getting organized and finding the routine that works for you.