It seems bento appears quite often in Sailor Moon. I've put up many pictures here, and have attempted to point out what foods are in the lunches, though it may not be entirely accurate.
Usagi looking at Naru's lunch.
Usagi's cute little lunch box!
Makoto is an great cook and enjoys making her own lunches. Looks like this one has onigiri, boiled eggs, veggies, and some sort of fried food.
A display of everyone's lunches at the cherry blossom picnic. Onigiri, fried shrimp, fruits and veggies, noodles, sushi, dumplings, eggs, sausages, and so much more!