One of the common foods found in a bento are tamagoyaki, which means a rolled omelet. I didn't make a tutorial for it, but I found a great one here. Definitely give it a try. I had alot of fun making it. In the tutorial they used 1 egg, but I used 2 with a little milk added into it. I guess you use however many eggs depending on how many people are eating. I used a small pan for making mine. Here are a few picks of my first attempt. I'll also include a mini recipe of the rice I made to go along with it.
Here's a picture of what it looks like as your "rolling" the omelet.
This is the rice I made to go along with it. I just used regular white rice to make it. Cook the rice normally and drain the water. Then sprinkle in some salt and sugar, pour in however much soy sauce you want, and add cilantro. It was very tasty and went well with the tamagoyaki.
I cut it into pieces.
Here's what it looks like on the inside. It is literally rolled into layers. I've seen a few variations where people put different veggies or meat into each layer. Have fun with it and enjoy!