I used to do simple bentos for myself in university.
* pocket sandwiches: spread filling in center of two slices of bread, squish with other side of a large circle cookie cutter, and then cut it out with the right side. Can be frozen in multiples.
* faux fried rice: cook rice, add frozen veggies, soy sauce, garlic powder. Stir together and microwave until hot. Was fast and easy, and can be done with leftover rice.
* real fruit jam: cook fruit of choice down, with a little water and sweetener of choice. It's done when it sticks to a spoon. (You can also add wine/mead to it.) Also good for getting rid of slightly soft fruit.
* preserving colour in fruit/fake Grapples: Take grape juice (I used white Welch's), and slice up apples. Stick 'em in the juice, and fish 'em out again. They taste like the grape juice and don't go brown at all.
* holding sauce in a seperate container: I used Kinder Surprise eggs (they are a chocolate egg that has a toy capsule inside), the capsule is really leak proof.
* cornbread muffins: Use sweet or savory cornbread and add whatever fillings you think will go great with 'em. I've had chopped up hot dogs in 'em. The best part is that they tuck nicely into the lunch box and can freeze well as well.