A Thermos or an insulated “food jar” (same idea) can hold hot soups and stews until lunchtime. Half of you are rolling your eyes right now because everybody knows this, while the other half are smacking your foreheads and going “oh, right, lunch foods can be hot instead of cold!” To those in the second group, welcome.
Redditor txgirlinbda has a few pro tips for packing soup. First, they suggest filling the container with hot or boiling water while you prepare the hot soup. (This helps to keep the food from cooling down as soon as it touches the container. For food safety reasons it’s best to keep the soup hotter than 140 degrees for as long as possible.) The other tip is to make sure you’re packing more of the “stuff” and less broth, both to make the soup more filling and to make it less splash-prone.