As someone who worked in a movie theater for four years, popcorn/candy is really not that big of a deal. Even in the biggest disasters (usually kids movies) you just break out the push broom and just walk down each row while someone else sweeps up at the aisles.
It’s the wet foods that are actually annoying. Nacho cheese is the worst, because it smears all over the place. Then there’s the bodily fluids…
Also, the people who clean between shows are called ushers. Janitors come early in the morning to vacuum, mop the floors and clean the bathrooms.