Castles and Crusades: What do I NEED to buy?

I'm at a nexus.  My mac had an update crisis at the weekend and ate my campaign world.  After a little bit of a cry, I came to the thinking that within this dark cloud lies the silver lining of opportunity.  I've been dissapointed with my experiences of DM'ing my campaign world with D&D 3.5 for a while so I'm off to Dragonmeet 2010 to buy Castles and Crusades.  I know I'll need the Players Handbook and probably Monsters and Treasure but is there anything else out there for C&C that I should definitely buy?