What should I buy with a $20 gift card from Target?

I have a 20$ gift card from target. What should I buy? I have an ipod nano 4th generation, have a samsung flight cellphone and I don't have a camera or lab top of any kind if that helps. I wear a size small in Juniors and I am 14 years old. I enjoy playing the Nancy Drew computer mystery games. Im not a big board game player. I don't know what to buy. Help!