Each of us brought one carry-on sized suitcase, youngest kid is 11 and could handle it OK except needed help lifting it into overhead racks on plane. Was a nice simple system for everyone to keep track of their own clothes, teddy bears, etc. Saved some $$$ on checked baggage fees and left nothing to the mercy of baggage handlers.
Dad carried a laptop case which contained a small netbook for checking email, storing photos, etc. plus a power bar and all required power chargers for phones, MP3s, etc. extra camera batteries and all other gadgets. Every night at the hotel we charged batteries, every day put all the gadgets in the laptop case and kept it in our our double-locked trunk while at the theme parks.
Mom carried a small backpack as her "purse" containing vital prescription drugs and other must-haves, kept it in her hands and stowed in front of her on the plane.
iPod Touch is a great little device for checking emails, etc. online with the WiFi capability - if your hotel has it.
Compiled a duo tang binder containing printouts of all tickets, reservations, passports, credit card #s, etc. Photocopied it and carried extra copy in a different suitcase.
Made another binder with touring plans, maps printed from google showing how to get to hotel, airport, parks plus with stores, restaurants and gas stations highlighted so we could find them easily (bringing a GPS from home would probably also work, but I don't own one). This saved having to bring heavy "Unofficial Guide" on the trip.
Joined Budget's "fastbreak" plan, for free, and breezed through car rental pickup.
That's everything I know about packing and prep. Have fun!