When you say you want it to last 12+ hours, does that mean you want it to be still safe to eat if it is in no way refrigerated or insulated for 12 hours? Or will he be able to put it in a fridge or cooler or something after he gets to work? Trying to determine if you need a built in ice pack or something similar. Also, does he eat a lot? Boxes vary a lot in volume so if he's a big eater he'll need a fairly large box.

As far as versatile and sturdy I'd recommend a Monbento. Rectangular Square

There are parts under the lids for utensils and Monbento makes their own sauce cups, chopsticks, cultery, etc. that can fit into the boxes.

I don't have a fridge available to me at school so I just bring my bento boxes (and a few drinks!) in a personal cooler.