A great yet simple craft for the lower grades. You'll need one toilet paper tube for every 4 students. The rest of the materials are things already in the classroom. No extensive prep required, but the kids love the result.
Add this craft to tie in with any number of science lessons: Reptiles, adaptations, turtles & tortoises, camouflage, etc.
For older children, this can tack on to a larger writing project.