Nah, the body would just lose the body heat and get cold
I guess you could use them as a refrigerator but then they'd just be slightly below room temperature and your food would be gross...not to mention it's been inside someone x_x
Well it'll be processed and turned into a liquid mixture containing the remnants of whatever else you have eaten, bile, acid, and your own cells. Best case scenario for using the human body as an oven would be making yourself and anyone else massively sick. Worst case? You make everyone sick, suffer horribly and die. Side note just pre-chewing someone else's food is apparently fine and a common thing in select cultures.
I guess you could use them as a refrigerator but then they'd just be slightly below room temperature and your food would be gross...not to mention it's been inside someone x_x