When Beavis returns to the burning dumpster after running around the school track, there is a visible sweat stain around his collar. The sweat stain disappears in the next shot.
After the Fire has been extinguished, Beavis finds a lighter on the ground nearby. Beavis had, at the Fire's command, picked up all the trash in the alley. There was no lighter there after he had done so.
After Beavis has finished picking up all the recyclables in the alley, some backgrounds are reused that still show the cans and bottles strewn about.
The girls at the escape room say they need two people who are really smart and good at solving puzzles to fill out their group. They were previously planning on attempting the escape room with just the two of them, so they didn't need smart people, just a pair of warm bodies to fill out the minimum group size requirement.
Fire commands Beavis to pick up all the plastic bottles in the alley (and the surrounding streets). Beavis picks up more than just plastic bottles, but all the trash, including cans and paper.