HOT and WET! Yes, I know this may start a flurry of Humidity vs Dry Heat postings but...I'm from California and went to Orlando/Cruised in mid October-I nearly died from the humidity! This compounded by the fact that I am mandated as a card carrying holder of the redhead/fair skinned to wear some form of skin protecting clothing induced me to plan our subsequent trip in January!
Seriously, take clothes that breathe, if it's tie-dyed wash it a million times prior to leaving (or you will end up with kids that resemble easter eggs), and consider a hair style that does not require a curling iron or styling products (the curls melt and hair products as does makeup, will simply slide right out).
Invest in some KEEP COOL or MIGRANE ICE patches-both are adhesive strip that can be worn on your neck to help manage the heat-they work well beneath clothing too (I use them routinly for Community Theatre Productions beneath my costumes).
Cruise the DIZ boards for more information-these are true Floida-holics who can give you advise on what to bring for anytime of the year!
Stay cool, stay safe (wear that sunscreen!) and have fun. happy cruising!