Mark and cut the box with holes for the RFID antenna, speaker, and power cable.
Coat a plain cardboard box in glitter Mod Podge.
The Mod Podge also works as an adhesive! Use it to attach eyes (google image search) and fins (yellow file folder).
Once dry, assemble the box and install the electronics.
Using a stretchy scrap of fabric, stitch the speaker in place with yarn and a yarn needle. This is a good temporary speaker mount you can easily undo later and is recommended over hot glue!