Motoko's poster is of a movie called "Hachinin no samurai (The Eight Samurai)", a spoof of Seven Samurai (1954) (The Seven Samurai).
The long-lost item Shinobu found in the cave is a "shampoo hat", a special bathing hat for children who are too young to shampoo their own hair.
Some of the scenes in the cave are spoofs of the Indiana Jones movies. Examples: Keitaro getting squashed by a giant rolling boulder, the turtle cult made up of hundreds of Mecha Tamas.