Was just there in May 6 months pregnant. Here are my tips:
Talk to your OB before going. Get any pertinent medical records to bring with you. Don't forget to bring your OBs card (& pager number), just in case. Find out where the nearest medical facilities are (Celebration Hospital) and phone number, just in case. And don't forget those prenatal vitamins!!
Don't over-do it. Rest a lot. Stay hydrated. Avoid all restricted rides, they are clearly marked. Don't carry too much yourself. Let your DH handle the heavy loads, especially your older child. Don't forget to buy your personal water squirting fan before you get there. While October weather should be mild, it can still be hot as h**l!
Slowly build up your walking endurance. Be sure to wear the same shoes at the park as you do on your walks. Your feet, and the rest of your body, will thank you for it. For me that was my Nike cross trainers. Love those shoes.
Soak your feet in the tub at night. I added a foot soak in it. THAT worked miracles. And I normally walk 3.5 miles a day anyhow.
"Belly Bras" are supposed to be wonderful. I, personally, don't find them much of a difference to put up with the uncomfortableness of them. So many people swear by them though, I could just be weird. Besides, even if it doesn't help, it certainly won't hurt.
Make yourself famaliar with the locations of bathrooms, and go frequently. If you wait until the urge is strong, you'll encounter long lines, closed bathrooms, or far flung bathrooms.
Familiear yourself with restruants to avoid any diet restrictions or food aversions and satisfy any food cravings.
If at possible, stay on site. Preferably a hotel with exclusive bus service (AKL), a monorail hotel (CR, Poly, GF), or a resort with boat service (WL, WLV, Ft.Wilderness) just in case you need to get back quickly. Or drive/rent a car.
Wear loose, comfortable clothing. It makes such a huge difference. Especially the loose part.
That is all I can think of for now. If I remember anything else (that pregnant brain shrinking thing), I'll post it later.