At one convention when I was a teen (mid-70's), they had hamburgers for sale at lunchtime.
They cooked up the burgers, put them in buns, then wrapped them in aluminum foil. Then they put a couple hundred of these things in a big styrofoam chest.
By the time you got to the bottom layer of burgers in the chest, the last couple dozen were literally submerged in all the grease that had seeped out of the ones above them.
But, as I recall, people still requested burgers, and we just plucked them out, dried them off, and handed them over.
There were no burgers the following year.