Don't overdress, you are going to heat up fast in a 5K. You could bring an old t-shirt to wear before the start to keep warm and just toss it beforehand if they don't have a gear check.
Most races don't allow IPODs and to me they are for training. I think you miss the "race experience" if you have an IPOD. Plus, its a short race and seems like more hassle to me to carry it.
I think you should be able to get by without carrying water, unless maybe it were to be a 90 degree morning. Look at elite runners, they wouldn't be weighed down by carrying water. But take water from a water stop, though alot of 5ks don't have a stop because its a short race.
Hope you have a great run!
