Tiffins are your friend. I invested in one last year when JD started kindergarten, and the size I have, it will hold enough food for both kids for their warm meals, and the metal bowls stack on top of each other and slide into a thermos. (
like this one) It holds heat for the food items 6 hours or so. It says 5 on the packaging, but I have found items hot from 8am to 2 or 3pm. Granted, I put the items in fresh out of the oven/pot - so they're boiling/steaming hot when they go in.
Additionally, for soup days - we have something like
this for the kids. TB has a Mickey Mouse one (like
this, but it is red/black) on the way, and JD has one that is
Field of Animals brand. These versions range between 35 and 80 dollars or euro -- and it's crazy expensive, but I needed something terribly bad and considering it will have use for many years, I could justify it.
IF you can find them at a reasonable price, there are stainless steel containers you can use for your kitchen and wrap in towels to keep them warm for around 5 hours. Otherwise, you could do something like
these, and put them in thermal lunch box carriers like the ones Fit and Fresh make. Amazon has started carrying
stainless steel lunch ware.
If going that route, you will want to see this post at Lunchinabox about
Choosing the right size bento for your needs.