From top down:

1. Big fish eat little fish. This is a common proverb.
2. The small are steamrollered by the large. This is a mild absurdity, as different sized steamrollers with the same proportions don’t exist.
3. The condiments chasing bread or toast looks like an analogy, but it isn’t. Even more absurd with food sprouting cartoony legs to chase each other.
4. Images from the previous panels are randomly mixed to form a hopelessly undecipherable mishmash. Larson takes the game he’s played in his two previous panels to its ultimate conclusion, a fitting punchline to his joke. The surprised bug eyes of the driver accentuate the absurd situation he finds himself in, despite being part of the joke. He’s driving the smallest, most absurd version of the steamrollers.