First, make a quick bracelet to measure the correct length of your bangle. Cut a thin strip from cereal box cardboard, and wrap it around your wrist, leaving enough room to slide it off your hand. Mark the spot where the ends of the strip cross, and cut slits in each so you can slot them together. Trim the ends, leaving a half inch or so from the slit on each end.
Use Mod Podge to glue the overlapping ends together. I sandwiched another rectangle of cardboard between the two paper ends, but that's purely optional.
Wait for the glue to dry, and paint your bangle. Or collage it, or draw on it with markers, or dip it in paint... the possibilities are nearly endless!