Draw a school bus on the driveway or sidewalk! Take your cardboard box school bus and run around the yard, pretending to pick up your stuff animals or toys as passengers. Or, if you don't have a box, pretend to be in a school bus anyway, make all the sound effects for a bus and go around picking up stuffed animal/plastic figurine passengers.
Use bread, cheese, cheese spread, cream cheese, Cheeries, Oreos, Twinkies, graham crackers, oat squares cereal, sprinkles, icing, etc. to make a school bus!
Use what you have around the house to make a school bus! Construction paper, newspaper, wrapping paper, cardboard boxes from at-home deliveries, paper bags, cereal boxes, etc!