>How much empty space should I leave when packing for Devcon? What kind and how many goodies should I expect to haul back? I am planning to take a traveller backpack to devcon (one of those that zips open instead of a drawstring like a backwoods). It hold about as much as a normal suitcase. Should I bring a second one?

There is enough stuff in Orlando to get (not just at DevCon) that you will need another piece of luggage. Of course there are many places to buy luggage so you don't need to bring one. :-)