Individually packaged hot lunch delivery service
Cambros will keep your food hot for 4 hours. Expensive but worth every penny. For a cheaper version, try Rubbermaid Pro-serve hot boxes. They are lighter weight. We use both. Put your food in there right from the oven and when you take it out again, it's just as hot. Nothing to plug in.
I've used the freezer "Brick" that Cambro makes, but have never used the hot one. No, regular building bricks, the kind you get at Home Despot/Lowes for 99 cents ea. Wrap em up in foil and toss them in a regular oven-under-the-range. It won't affect your oven's performance--matter of fact it might even enhance the oven's performance.... I usually had 4 or 5 living in the oven f/t.
Make sure the hot brick sits in a hotelpan/ half sheetpan that's in the middle of the Cambro, in other words, make sure the brick doesn't rest on the bottom or touch the top, or it will melt the plastic. I've seen other guys fill a hotel pan with hot water for the same effect, but I find this much messier and more fiddly.