You can find sushi bento, but you find that sushi or raw fish will be very small portion of bento selection. First, average Japanese people do not eat sushi every day, not even every week. Also, bento is meant as take away lunch or dinner box. What inside of bento is meant to last for entire day to be eaten later.

For me it is 立ち食いうどん、そば, stand up Soba and Udon soup noodle shop, located at train stations. Just add tempura or croquette and make a quick meal to fill me up before catching a train. During cold winter season my favorite is curry udon!