Well, if it is an accessory you didn't know you needed, you may not need it, hehehe.
Put it in the piggy bank for the 29er.
Do you have enough biker shorts and wicking tops? You could buy some of those and it wouldn't go awry. I only have two pair of shorts and 3 shirts; I'm going to need to slowly build up my wardrobe so I don't have to do laundry so much.