I work at my kids' school and in the cafeteria supervision.
Just get, what your kids CAN open and close, by themselves and handle.
SO many kids, cannot even open or close, the lunch boxes they have.
Bento Boxes are good, because it has compartments. To separate the food especially if one has sauces or gravy etc.
You pack in it, what your kids, WILL eat.
BECAUSE: If they don't like what you pack, they will NOT eat... even if they are hungry.
I see this all the time at my kids' school... the Mom has a fancy cutsie lunch for their kid, but the kid does not like what the Mom packed... thus, the kid will NOT NOT NOT eat it, EVEN if they are hungry. And then they go ALL day, with NO food in their tummy... and it affects their mood and concentration all day. And school staff cannot "force" a kid to eat.
So... pack only what you KNOW your kid, will eat. Even if that is the same thing everyday. Many kids like and eat, the same thing everyday. Even if that is just a sandwich or cut up fruit or veggies with Ranch dressing as a dip.
AND be SURE to get, a blue-ice, ice pack, for the lunch bag. Otherwise, the food will not stay cool at an adequate temperature. And then, the kid cannot eat it because the food will spoil.
I see so many kids, that have NO ice pack in their lunch bag, and they have a yogurt cup in there or a bottle of milk, and then it is all warm and they can't eat it. Because, the Mom does not put an ice-pack in their lunch bag. And their lunch bag is not even insulated.
Just get, a good INSULATED lunch bag.
AND a blue-ice, ice pack.
And a lunch food container.
For insulated lunch bags, the brand "Igloo" is good.
They have all kinds of styles and prices and it is well made.
Just look online.
Another Tip:
Make sure, that with a Sharpie pen permanent marker, put your kids' name, ON the lunch box, AND on the lunch containers, AND on the water bottle etc., that your kid has. Because, these things gets lost or forgotten, all the time, by kids at school. And if their name is not on it, then you will not get it back.
You can write their first name and last name initial, on it.
Or also put a luggage tag on it, with their name.
As for what to pack in their lunch: well, just pack what your kids like and will eat. It can be anything. Except not candy. Although kids bring that in their lunch bag too, all the time.
And make sure that nut products or peanuts/peanut butter, is or is not allowed at your kids' school. And if it is not allowed, you cannot make Peanut butter sandwiches.
Another Tip:
whatever lunch containers you get... make SURE that it WILL fit, in your kids' lunch bag. Some kids come to school, with lunch containers that are too big or long, to even fit in their lunch bag. And then, the ice pack won't even fit in it, either.
Pasta is a good easy thing, to pack for kids' lunch.
Or sandwiches
Or pita sandwiches
or, deli meats and crackers and cheese.
Or left overs
Or cut up fruit or veggie sticks
Things that are EASY for the kid to eat and handle, and that they WILL eat, AND like.
Another tip: I see so many young ones, come to school with an orange or Clementine mandarin orange. Fine. The kid likes it and will eat it. BUT the problem is: the Mom, just sends the whole orange to school with the kid. It is NOT even, peeled. And especially with the young kids/Kindergarten etc., they cannot even peel it themselves. So then, the school staff spends the lunch period, going around peeling oranges for each kid. SO the tip is: if you pack this sort of thing, PEEL it beforehand, at home... and put it in a little Ziplock or plastic container, for your kid, for lunch. Prep... the food you send your kid to school with. Cut things up into sizes that a kid, can eat. Reasonably.