People are often a lot more interested in hot meals, and my kids are no exception. I've tried a bunch of options here including putting rocks in thermoses (turns out kindergarteners worry more than you might think about whether they'll accidentally eat rocks that are bigger than their mouths), bringing a microwave and toaster (good, but too bulky for school especially when you count the battery), and ramen (great, but Lily only likes one kind and I'm worried she'll get sick of it). We recently got an electric lunchbox (this one because it was on sale, but there are a bunch) and it's pretty great!

It's insulated, and we prepare it the night before and put it in the fridge:

In the morning I set the timer:

It only goes up to 4hr, perhaps for danger zone reasons, but since the kids leave at 8am and lunch is at 12:30 that's just right (4hr timer, 30min heating).

When the timer gets to zero it starts heating, and counts down from 30min (by default; adjustable):

Tastes marginally better than microwave food, and loads better than cold food.

I haven't yet tested if it's powerful enough to handle frozen food. I hope it is, since then you could prepare it whenever and leave it in the freezer until ready to eat.

I also wonder if it could bake bread. It only goes up to 90C and it be a bit like steamed bread, but freshness might outweigh texture here.