You can hold the CPX boards in your palms and use a USB power or AAA battery box, or, dress things up a bit with Circuit Playground Express enclosures and some watch bands or straps for a more secure option suitable for a costume!
To assemble, first open the CPX enclosure and thread the band, strap, or string through the slots.
Then, place the CPX into the case and close it.
Now, plug the AAA battery pack into the CPX.
Hook the battery pack to the strap, and secure it to your hand.