Preheat the jar and wrap it tight

Without a thermos you’re not going to get truly hot soup at 1 p.m., but you can get close if you start hot and build an insulation nest around it.

The trick is to make the container do the thermos’s job. A wide-mouth glass jar works great. Fill it with boiling water, put the lid on, let it sit for a few minutes, then dump that water out. You’ve just preheated the jar, so it won’t steal heat from your food the second you pour it in.

Then fill it with the hottest food you can manage. Soup should be nearly boiling. Pasta should get a little extra sauce or broth so it doesn’t glue itself into one mass. Screw the lid on, but vent it for a minute first if the food is super hot so pressure doesn’t build up.

Now wrap the whole thing in a couple of folded kitchen towels, or even a sweatshirt, and put it in an insulated lunch bag. That towel layer is doing the real insulating work. If you just toss a hot jar into a plain lunchbox, it’ll be warm for maybe an hour.

If you need piping hot after four or five hours, buy a thermos. But for a lunch you’ll eat in a couple hours, the preheat-and-wrap method is completely fine.

Lukewarm spaghetti is a sad way to learn you forgot the preheat step.