My two favorite projects were the Giant Centipede and the Mosquito.

For the Giant Centipede maybe you can use string to make the centipede curl up. Because with string when you pull it will make it curl. You could also add legs and try to simulate how its legs can move independently. You should also find out how the separate parts of the centipede work together to curl up.

For the Mosquito, if you have time you can add independent movement like its wings flapping or its head moving side to side. You can also try to show how this is effective in reality as mosquitos breed in trash and small puddles so maybe try to make an environment that shows this. On top of all this, you can also try to find what materials will float and list them to find what works.