You will lose your place in line, which could result in a longer wait before you get your watch (although Apple has said many people will get the watch earlier than expected).
The rubber band is only $50, the leather is more depending which you are looking at-- you could always order the leather band separately, that way you have the rubber one if you go the the gym or have a more casual need, and you can swap for the leather as appropriate as well.
I ordered the SS with bland sport band, and a separate Malenese.