Originally Posted by cpu121:
“We just place them on a hotplate and serve when we're ready - most of the time the venues just have a sink and a kettle in the kitchen so everything has to prepared beforehand. The journeys are short enough that the food doesn't cool down a lot; it's just spilling the contents on the way that we're worried about.”
Maybe pressure cookers are your best bet. Although they may be more expensive than other options (if there are any), there are models which don't have weights to fall off and which seal perfectly.
I'd recommend
Kuhn Rikon models. You can cook the soups and stuff in them much faster as well. The pressure seems to keep the food much hotter for longer if you don't release the steam, as pressure cookers hold the temperature at well above boiling point - this may not be good for some foods which can overcook of course.