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.
Episode 4
Usagi looking at Naru's lunch.
Episode 17
Usagi's cute little lunch box!
Ami's lunch of sandwiches.
Episode 25
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 dessert bento with fruit. I like how they carve their apple slices to look like rabbits. Funny that the lid had Snoopy and Woodstock on it.
Some carry their bento boxes in cloth pouches.
Usagi drooling over Mako's onigiri.
Usagi carries her lunch in a cute cloth pouch.
Episode 51
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!
The lunch Naru made for her boyfriend Umino. Rice, omelet, veggies, octo-sausage, rolls.