Assuming it isn't a performance (e.g. magic show) within a performance (the play), I would think the character would need to do quick visual effects. Without knowing the play, it is hard to give you a good sense of what would work. I think it would be great if the character does magic when none of the other characters are looking and then acts like nothing happened (so only the audience would know what happened).
General ideas:
Appearing anything (cane, rose)
Dancing anything (hankie. cane)
Floating anything (sunglasses, rose)
Disappearing anything (using TT or Pull or Gecko)
Any of the Airborne effects