Here are a few I've done
For 3D shapes, spend some time exploring. Students record the number of faces, edges, and corners. Point out non-defining attributes (it is a cube because it's blue, or small? No! It's a cube because it has 8 corners, etc...). Then build 3d shapes with toothpicks (edges) and gumdrops (corners). You'll have to show how the faces are invisible here. You can also have kids go on a scavenger hunt in the classroom to find 3D shapes or 3D shapes.
Spend time building new 2D shapes with other 2D shapes, then recording (I built a trapezoid using 3 triangles, I built a pentagon using 1 trapezoid and 1 triangle, etc.).