Ooh I have such a hard time trying to get the bento filled.
I like adding potstickers because you all ways get a lot when you buy or make them and they're fast to cook. They also add meat, which I find is always hard to add.
I also like boiling brocolli for 2 minutes then filling in gaps with them.
Honestly you should see what you have in your cabnets and fridge. I ended up wrapping carrots with egg for a bento for my friend as filler and she liked it. Bentos are good to experiment with flavors.
Do you think a bento box that's 3inX2inX2in is too small?