South Florida Trip: What to Pack for Early January Weather?

I will be in Ft. Lauderdale, Miami and South Beach for 5 days on vacation the first week of January. I am not sure what to pack. I am on a college student's budget of what i can buy for the trip. I plan on going out a few nights (a nice dinner one night) and hopefully a trip to the beach if the weather allows. I want to get some sightseeing in as well, and any recommendations for what to see would be welcome! HELP!