I've found that one of my bento box can hold just enough food to last me through my work day. Usually by the time I head home my tummy's rumbling a little and when I get home I need a snack before bed. If I make 1.5 bento boxes worth of food it's enough to last me the entire work day and I can usually skip dinner.
I really like making onigiris (rice balls), it's a lot of fun using the nori (seaweed) and cutting it to make emoticon-onigiris or animal onigiris. Japanese rice is really sticky though, if I'm not careful it has a tendency to get all over the place. Now I use saran wrap so my hand don't actually touch the rice, otherwise no matter how much salt or water I put on my hands it still sticks and my onigiris turn out warped and weird looking. Next challenge is to try making onigiris that have a filling inside instead of just plain rice :3