Ensure the Circuit Playground has the battery attached to the back with the adhesive found earlier. Then put adhesive on the battery and put in the bottom of the short can. Turn the battery pack on to light the Circuit Playground NeoPixels.
Slip the short can onto the end of the longer can. It's a tight fit but the slit will allow it to fit snugly.
Let's first see the long can lined with mylar film. Remember shiny is good:
Now to replace the mylar with aluminum foil. Curl the foil into a cylinder with the shiniest side inside the middle. If the foil crinkles a bit, that is ok as it will lend irregular reflections. Ensure it does not have any big bubbles. You can use glue stick to secure to the can interior or clear tape.
Rotate the small can on the end and the lightshow will change. Beautiful.
There are many ways to cause the light to refract differently. You can take the Pringle can lids and put colored beads between them. You can then fit this inside the kaleidoscope. You can also use a sharp edge to make a star pattern into a lid and slip it on the end. You can try a magnifying glass or jar bottom on the end. Anything that might bend the light in ways that make the light appear in interesting shapes. The house is your source for materials, many of which may be found in the kitchen.
Experiment with different lighting effects. Blinking or grdient color patterns may look good. Just don't make it too bright which might hurt your eyes. The minimum value for brightness the board likes to see is about 16.
The cans may be painted or you can glue/tape construction paper or wrapping paper to the cans.
When you need your Circuit Playground back, just take the short tube off the longer one, and pull the board and battery out. You can always put it back in later.